Bacteria total maximum daily loads for the lower Bird Creek watershed area (OK1213000010010_00)

              FINAL
BACTERIA TOTAL MAXIMUM DAILY LOADS FOR THE LOWER BIRD CREEK WATERSHED AREA (OK121300010010_00)
Prepared by:
INDIAN NATIONS COUNCIL OF GOVERNMENTS
OKLAHOMA DEPARTMENT OF ENVIRONMENTAL QUALITY
JULY 2011 FINAL
BACTERIA TOTAL MAXIMUM DAILY LOADS FOR THE LOWER BIRD CREEK WATERSHED AREA (OK121300010010_00)
OKWBID
OK121300010010_00, OK121300010090_00
OK121300010060_00
Prepared by:
INDIAN NATIONS COUNCIL OF GOVERNMENTS
OKLAHOMA DEPARTMENT OF ENVIRONMENTAL QUALITY
JULY 2011
Lower Bird Creek Bacteria TMDLs Table of Contents
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TABLE OF CONTENTS
EXECUTIVE SUMMARY ...................................................................................................... v
SECTION 1 INTRODUCTION ............................................................................................. 1-1
1.1 TMDL Program Background ..................................................................................... 1-1
1.2 Watershed Description ............................................................................................... 1-2
SECTION 2 PROBLEM IDENTIFICATION AND WATER QUALITY TARGET ...... 2-1
2.1 Oklahoma Water Quality Standards ........................................................................... 2-1
2.2 Problem Identification ................................................................................................ 2-4
2.3 Water Quality Target .................................................................................................. 2-6
SECTION 3 POLLUTANT SOURCE ASSESSMENT ....................................................... 3-1
3.1 NPDES-Permitted Facilities ....................................................................................... 3-1
3.1.1 Continuous Point Source Discharges ............................................................. 3-1
3.1.2 No-Discharge Facilities and SSOs ................................................................. 3-5
3.1.3 NPDES Municipal Separate Storm Sewer Discharge (MS4) ......................... 3-7
3.1.4 Concentrated Animal Feeding Operations ..................................................... 3-8
3.2 Nonpoint Sources ....................................................................................................... 3-9
3.2.1 Wildlife ........................................................................................................... 3-9
3.2.2 Non-Permitted Agricultural Activities and Domesticated Animals ............. 3-10
3.2.3 Failing Onsite Wastewater Disposal Systems and Illicit Discharges ........... 3-12
3.2.4 Domestic Pets ............................................................................................... 3-14
3.3 Summary of Bacteria Sources .................................................................................. 3-14
SECTION 4 TECHNICAL APPROACH AND METHODS .............................................. 4-1
4.1 Using Load Duration Curves to Develop TMDLs ..................................................... 4-1
4.2 Development of Flow Duration Curves ..................................................................... 4-2
4.3 Estimating Current Point and Nonpoint Loading ....................................................... 4-3
4.4 Development of TMDLs Using Load Duration Curves ............................................. 4-3
SECTION 5 TMDL CALCULATIONS ................................................................................ 5-1
5.1 Flow Duration Curves ................................................................................................ 5-1
5.2 Estimated Loading and Critical Conditions ............................................................... 5-3
5.3 Wasteload Allocation ................................................................................................. 5-6
5.4 Load Allocation .......................................................................................................... 5-7
5.5 Seasonal Variability .................................................................................................... 5-7
5.6 Margin of Safety ......................................................................................................... 5-7
5.7 TMDL Calculations .................................................................................................... 5-8
5.8 LDCs and TMDL Calculations for Additional Bacterial Indicators ........................ 5-12
5.8 Reasonable Assurances ............................................................................................ 5-15 Lower Bird Creek Bacteria TMDLs Table of Contents
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SECTION 6 PUBLIC PARTICIPATION ............................................................................ 6-1
SECTION 7 REFERENCES .................................................................................................. 7-1
APPENDICES
Appendix A Ambient Water Quality Bacteria Data – 2005 to 2009
Appendix B NPDES Permit Discharge Monitoring Report Data and Sanitary Sewer Overflow Data
Appendix C Estimated Flow Exceedance Percentiles
Appendix D State of Oklahoma Antidegradation Policy
Appendix E Storm Water Permitting Requirements and Presumptive Best management Practices (BMP) Approach
Appendix F Response to Comments
LIST OF FIGURES
Figure 1-1a Watersheds Not Supporting Primary Body Contact Recreation Use within the Study Area ...................................................................................................... 1-4
Figure 1-1b Coal and Ranch Watersheds……………………………………………………..1-5
Figure 1-2 Land Use Map by Watershed ............................................................................... 1-7
Figure 3-1a Locations of NPDES-Permitted Facilities and MS4s in the Study Area .............. 3-2
Figure 3-1b MS4s in the Coal and Ranch Watersheds ........................................................... 3-23
Figure 5-1 Primary Season Flow Duration Curve Bird Creek Near Catoosa ........................ 5-1
Figure 5-2 Primary Season Flow Duration Curve Coal Creek ............................................... 5-2
Figure 5-3 Primary Season Flow Duration Curve Ranch Creek ............................................ 5-2
Figure 5-4 Primary Season Enterococci Load Duration Curve Bird Creek Near Catoosa .... 5-4
Figure 5-5 Primary Season E. Coli Load Duration Curve for Coal Creek ............................. 5-4
Figure 5-6 Primary Season E. Coli Load Duration Curve for Ranch Creek .......................... 5-5
Figure 5-7 Primary Season Fecal Coliform Load Duration Curve for Lower Bird Creek ... 5-13
Figure 5-8 Primary Season E. Coli Load Duration Curve for Lower Bird Creek ................ 5-14
LIST OF TABLES
Table ES-1 Excerpt from the 2008 Integrated Report – Comprehensive Waterbody Assessment Category List ..................................................................................... vii
Table ES-2 Summary of Indicator Bacteria Samples from Primary Contact Recreation Season, 2003-2009 ............................................................................................................. viii
Table ES-3 TMDL Percent Reductions Required to Meet Water Quality Standards for Impaired Waterbodies in the Study Area ............................................................. xiv
Table ES-4 TMDL Summaries Examples ................................................................................ xv Lower Bird Creek Bacteria TMDLs Table of Contents
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Table 1-1 Water Quality Monitoring Stations used for 2008 303(d) Listing Decision ........ 1-2
Table 1-2 County Population and Density ............................................................................ 1-3
Table 1-3 Average Annual Precipitation by Watershed ....................................................... 1-3
Table 1-4 Land Use Summaries by Watershed ..................................................................... 1-6
Table 2-1a Excerpt from the 2008 Integrated Report – Comprehensive Waterbody Assessment Category List .................................................................................... 2-1
Table 2-1b Designated Beneficial Uses for Each Impaired Streams in the Study Area ......... 2-1
Table 2-2 Summary of Indicator Bacteria Samples from Primary Contact Recreation Season, 2005-2009 ............................................................................................................. 2-5
Table 2-3 Waterbodies Requiring TMDLs for Not Supporting Primary Contact Recreation Use ........................................................................................................................ 2-5
Table 3-1 Point Source Discharges in the Study Area .......................................................... 3-2
Table 3-2 NPDES No-Discharge Facilities in the Study Area ............................................. 3-5
Table 3-3 Sanitary Sewer Overflow Summary ..................................................................... 3-6
Table 3-4 NPDES-Permitted CAFOs in Study Area ............................................................ 3-8
Table 3-5 Estimated Deer Populations ............................................................................... 3-10
Table 3-6 Estimated Fecal Coliform Production for Deer .................................................. 3-10
Table 3-7 Commercially Raised Farm Animals and Animal Per Acre Estimates by Watershed……………………………………………………………………...3-12
Table 3-8 Estimated Poultry Numbers for Contract Growers Inventoried by ODAFF ...... 3-11
Table 3-9 Fecal Coliform Production Estimates for Commercially Raised Farm Animals (x109 number/day) .............................................................................................. 3-12
Table 3-10 Estimates of Sewered and Unsewered Households ............................................ 3-13
Table 3-11 Estimated Fecal Coliform Load from OSWD Systems ...................................... 3-14
Table 3-12 Estimated Numbers of Pets ................................................................................ 3-14
Table 3-13 Estimated Fecal Coliform Daily Production by Pets (x 109) .............................. 3-14
Table 3-14 Estimated Major Source of Bacteria Loading by Watershed ............................. 3-15
Table 3-15 Summary of Fecal Coliform Load Estimates from Nonpoint Sources to Land Surfaces .............................................................................................................. 3-15
Table 5-1 TMDL Percent Reductions Required to Meet Water Quality Standards for Impaired Waterbodies in the Study Area .............. Error! Bookmark not defined.
Table 5-2 Wasteload Allocations for NPDES-Permitted Facilities ...................................... 5-7
Table 5-3 TMDL Summary Examples ................................................................................. 5-9
Table 5-4 Enterococci TMDL Calculations for Lower Bird Creek .................................... 5-10
Table 5-5 E. coli TMDL Calculations for Coal Creek ....................................................... 5-11
Table 5-6 E. coli TMDL Calculations for Ranch Creek .................................................... 5-12 Lower Bird Creek Bacteria TMDLs Table of Contents
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Table 5-7 Fecal Coliform TMDL Calculations for Lower Bird Creek ............................... 5-13
Table 5-8 E. coli TMDL Calculations for Lower Bird Creek ............................................ 5-14
Table 5-9 Partial List of Oklahoma Water Quality Management Agencies ....................... 5-15 Lower Bird Creek Bacteria TMDLs Acronyms and Abbreviations
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ACRONYMS AND ABBREVIATIONS
ASAE
American Society of Agricultural Engineers
BMP
best management practice
CAFO
Concentrated Animal Feeding Operation
CFR
Code of Federal Regulations
cfs
Cubic feet per second
cfu
Colony-forming unit
CPP
Continuing planning process
CWA
Clean Water Act
DMR
Discharge monitoring report
LA
Load allocation
LDC
Load duration curve
mg
Million gallons
mgd
Million gallons per day
mL
Milliliter
MOS
Margin of safety
MS4
Municipal separate storm sewer system
NPDES
National Pollutant Discharge Elimination System
O.S.
Oklahoma statutes
ODAFF
Oklahoma Department of Agriculture, Food and Forestry
ODEQ
Oklahoma Department of Environmental Quality
OPDES
Oklahoma Pollutant Discharge Elimination System
OSWD
Onsite wastewater disposal
OWRB
Oklahoma Water Resources Board
PBCR
Primary body contact recreation
PRG
Percent reduction goal
SSO
Sanitary sewer overflow
TMDL
Total maximum daily load
USDA
U.S. Department of Agriculture
USEPA
U.S. Environmental Protection Agency
USGS
U.S. Geological Survey
WLA
Wasteload allocation
WQM
Water quality monitoring
WQS
Water quality standard(s)
WWTP
Wastewater treatment plant
Lower Bird Creek Bacteria TMDLs Executive Summary
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Executive Summary
This report documents the data and assessment used to establish TMDLs for the pathogen indicator bacteria fecal coliform, Escherichia coli (E. coli), and Enterococci within the Lower Bird Creek watershed. Elevated levels of pathogen indicator bacteria in aquatic environments indicate that a receiving waterbody is contaminated with human or animal feces and that there is a potential health risk for individuals exposed to the water. Data assessment and TMDL calculations are conducted in accordance with requirements of Section 303(d) of the Clean Water Act (CWA), Water Quality Planning and Management Regulations (40 CFR Part 130), U.S. Environmental Protection Agency (USEPA) guidance, and Oklahoma Department of Environmental Quality (ODEQ) guidance and procedures. ODEQ is required to submit all TMDLs to USEPA for review and approval. Once the USEPA approves a TMDL, then the waterbody may be moved to Category 4a of a state’s Integrated Water Quality Monitoring and Assessment Report, where it remains until compliance with water quality standards (WQS) is achieved (USEPA 2003).
The purpose of this report is to establish pollutant load allocations for indicator bacteria in impaired waterbodies, which is the first step toward restoring water quality and protecting public health. TMDLs determine the pollutant loading a waterbody can assimilate without exceeding the WQS for that pollutant. A TMDL consists of a wasteload allocation (WLA), load allocation (LA), and a margin of safety (MOS). The WLA is the fraction of the total pollutant load apportioned to point sources, and includes stormwater discharges regulated under the National Pollutant Discharge Elimination System (NPDES) as point sources. The LA is the fraction of the total pollutant load apportioned to nonpoint sources. The MOS is a percentage of the TMDL set aside to account for the lack of knowledge associated with natural processes in aquatic systems, model assumptions, and data limitations.
This report does not stipulate specific control actions (regulatory controls) or management measures (voluntary best management practices) necessary to reduce bacteria loadings within each watershed. Watershed-specific control actions and management measures will be identified, selected, and implemented under a separate process.
E.1 Problem Identification and Water Quality Target
A decision was made to place the three waterbodies, listed in Table ES-1, on the ODEQ 2008 303(d) list because evidence of nonsupport of primary body contact recreation (PBCR) was observed.
Elevated levels of bacteria above the WQS for any of the three bacterial indicators resulted in the requirement that a TMDL be developed. The TMDLs established in this report are a necessary step in the process to develop the bacteria loading controls needed to restore the primary body contact recreation use designated for these waterbodies.
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Table ES-1 Excerpt from the 2008 Integrated Report – Comprehensive Waterbody Assessment Category List Waterbody ID Waterbody Name Stream Miles Category Priority TMDL Date Primary Body Contact Recreation Fecal Coliform E.coli Enterococci
OK121300010010_00
Bird Creek (Lower)
23.8
5a
1
2010
N
X
X
X
OK121300010090_00
Coal Creek
6.71
5a
1
2010
N
X
OK121300010060_00
Ranch Creek
6.94
5a
1
2010
N
X
N = Not Supporting; Source: 2008 Integrated Report, ODEQ 2008
There are two bacteria monitoring programs for which data were used in this report for the Lower Bird Creek. The first is the OWRB’s Beneficial Use Monitoring Program (BUMP) site at Highway 266 bridge (OWRB BUMP ID OK121300010010-001AT), the same location as the USGS stream gage. The only bacteria BUMP data for this site was during 2006, and all three indicators were monitored during this time. The second data set was from stream monitoring by the City of Tulsa, but only fecal coliform data was monitored by Tulsa. Tulsa’s fecal coliform data from 2005 to 2009 from the nearest site to the BUMP station was used. This site is labeled by Tulsa as site BC-5b. For the fecal coliform dataset, the Tulsa 2005-09 and OWRB 2006 data were combined into a single data set. For the data collected between 2005 and 2009 and the re-assessment for PBCR use conducted for this study, evidence of nonsupport of the PBCR use based upon all three indicators was observed in the waterbody. There is one Oklahoma Conservation Commission monitoring site each on Coal and Ranch Creeks.
Table ES-2 summarizes the waterbodies requiring the TMDLs for not supporting PBCR as a result of the data re-assessment by this study. Only data from each year’s primary contact recreation period (May 1 through September 30) was used in the assessment and TMDLs. The data summary in Table ES-2 provides a general understanding of the amount of water quality data available and the severity of exceedances of the water quality criteria. This data set includes the data used to support the decision to place specific waterbodies within the Study Area on the ODEQ 2008 303(d) list (ODEQ 2008). It also includes the new date collected after the data cutoff date for the 2008 303(d) list. Lower Bird Creek Bacteria TMDLs Executive Summary
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Table ES-2 Summary of Indicator Bacteria Samples from Primary Contact Recreation Season, 2003-2009* Waterbody ID Waterbody Name Indicator Bacteria** Single Sample Water Quality Criterion (#/100ml) Geometric Mean Concentration (count/100ml) Number of Samples Number of Samples Exceeding Single Sample Criterion % of Samples Exceeding Single Sample Criterion Notes**
OK121300010010_00
Bird Creek (Lower) FC
400
367
54
23
43%
TMDL needed EC
406
205
10
4
40%
TMDL needed ENT
108
170
10
5
50%
TMDL needed
OK121300010090_00
Coal EC
406
271
10
4
40%
TMDL needed
OK121300010060_00
Ranch EC
406
167
13
4
31%
TMDL needed
EC = E. coli; ENT = Enterococci; FC = fecal coliform. *2005-2009 for Bird Creek (Lower).
**Highlighted bacteria indicators require TMDL. Lower Bird Creek Bacteria TMDLs Executive Summary
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The definition of PBCR is summarized by the following excerpt from Chapter 45 of the Oklahoma WQS (OWRB 2008a).
(a) Primary Body Contact Recreation involves direct body contact with the water where a possibility of ingestion exists. In these cases the water shall not contain chemical, physical or biological substances in concentrations that are irritating to skin or sense organs or are toxic or cause illness upon ingestion by human beings.
(b) In waters designated for Primary Body Contact Recreation...limits...shall apply only during the recreation period of May 1 to September 30. The criteria for Secondary Body Contact Recreation will apply during the remainder of the year.
To implement Oklahoma’s WQS for PBCR, the Oklahoma Water Resources Board (OWRB) promulgated Chapter 46, Implementation of Oklahoma’s Water Quality Standards (OWRB 2008b). The excerpt below from Chapter 46: 785:46-15-6, stipulates how water quality data will be assessed to determine support of the PBCR use as well as how the water quality target for TMDLs will be defined for each bacterial indicator.
(a) Scope. The provisions of this Section shall be used to determine whether the subcategory of Primary Body Contact of the beneficial use of Recreation designated in OAC 785:45 for a waterbody is supported during the recreation season from May 1 through September 30 each year. Where data exist for multiple bacterial indicators on the same waterbody or waterbody segment, the determination of use support shall be based upon the use and application of all applicable tests and data.
(b) Screening levels:
(1) The screening level for fecal coliform shall be a density of 400 colonies per 100ml.
(2) The screening level for Escherichia coli shall be a density of 235 colonies per 100 ml in streams designated in OAC 785:45 as Scenic Rivers and in lakes, and 406 colonies per 100 ml in all other waters of the state designated as Primary Body Contact Recreation.
(3) The screening level for Enterococci shall be a density of 61 colonies per 100 ml in streams designated in OAC 785:45 as Scenic Rivers and in lakes, and 108 colonies per 100 ml in all other waters of the state designated as Primary Body Contact Recreation.
(c) Fecal coliform:
(1) The Primary Body Contact Recreation subcategory designated for a waterbody shall be deemed to be fully supported with respect to fecal coliform if the geometric mean of 400 colonies per 100 ml is met and no greater than 25% of the sample concentrations from that waterbody exceed the screening level prescribed in (b) of this Section.
(2) The parameter of fecal coliform is not susceptible to an assessment that Primary Body Contact Recreation is partially supported.
(3) The Primary Body Contact Recreation subcategory designated for a waterbody shall be deemed to be not supported with respect to fecal coliform if the geometric mean of 400 colonies per 100 ml is not met, or greater than 25% of the sample concentrations from that waterbody exceed the screening level prescribed in (b) of this Section, or both such conditions exist. Lower Bird Creek Bacteria TMDLs Executive Summary
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(d) Escherichia coli (E. coli):
(1) The Primary Body Contact Recreation subcategory designated for a waterbody shall be deemed to be fully supported with respect to E. coli if the geometric mean of 126 colonies per 100 ml is met, or the sample concentrations from that waterbody taken during the recreation season do not exceed the screening level prescribed in (b) of this Section, or both such conditions exist.
(2) The parameter of E. coli is not susceptible to an assessment that Primary Body Contact Recreation is partially supported.
(3) The Primary Body Contact Recreation subcategory designated for a waterbody shall be deemed to be not supported with respect to E. coli if the geometric mean of 126 colonies per 100 ml is not met and any of the sample concentrations from that waterbody taken during the recreation season exceed a screening level prescribed in (b) of this Section.
(e) Enterococci:
(1) The Primary Body Contact Recreation subcategory designated for a waterbody shall be deemed to be fully supported with respect to Enterococci if the geometric mean of 33 colonies per 100 ml is met, or the sample concentrations from that waterbody taken during the recreation season do not exceed the screening level prescribed in (b) of this Section, or both such conditions exist.
(2) The parameter of Enterococci is not susceptible to an assessment that Primary Body Contact Recreation is partially supported.
(3) The Primary Body Contact Recreation subcategory designated for a waterbody shall be deemed to be not supported with respect to Enterococci if the geometric mean of 33 colonies per 100 ml is not met and any of the sample concentrations from that waterbody taken during the recreation season exceed a screening level prescribed in (b) of this Section.
Compliance with the Oklahoma WQS is based on meeting requirements for all three bacterial indicators. Where concurrent data exist for multiple bacterial indicators on the same waterbody or waterbody segment, each indicator group must demonstrate compliance with the numeric criteria prescribed (OWRB 2008a).
As stipulated in the WQS, utilization of the geometric mean to determine compliance for any of the three indicator bacteria depends on the collection of five samples within a 30-day period. For most waterbodies in Oklahoma there are insufficient data available to calculate the 30-day geometric mean since most water quality samples are collected once a month. As a result, waterbodies placed on the 303(d) list for not supporting the PBCR are the result of individual samples exceeding the instantaneous criteria or the long-term geometric mean of individual samples exceeding the geometric mean criteria for each respective bacterial indicator. Targeting the instantaneous criterion established for the primary contact recreation season (May 1st to September 30th) as the water quality goal for TMDLs corresponds to the basis for 303(d) listing and may be protective of the geometric mean criterion as well as the criteria for the secondary contact recreation season. However, both the instantaneous and geometric mean criteria for E. coli and Enterococci will be evaluated as water quality targets to ensure the most protective goal is established for each waterbody. Lower Bird Creek Bacteria TMDLs Executive Summary
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All TMDLs for fecal coliform must take into account that no more than 25 percent of the samples may exceed the instantaneous numeric criteria. For E. coli and Enterococci, no samples may exceed instantaneous criteria. Since the attainability of stream beneficial uses for E. coli and Enterococci is based on the compliance of either the instantaneous or a long-term geometric mean criterion, percent reductions goals will be calculated for both criteria. TMDLs will be based on the percent reduction required to meet either the instantaneous or the long-term geometric mean criterion, whichever is less.
E.2 Pollutant Source Assessment
A source assessment characterizes known and suspected sources of pollutant loading to impaired waterbodies. Sources within a watershed are categorized and quantified to the extent that information is available. Bacteria originate from warm-blooded animals and sources may be point or nonpoint in nature.
There are three NPDES-permitted municipal wastewater treatment plants (WWTPs) in the contributing watersheds of Lower Bird Creek (OK121300010010_00). There are no WWTPs in the contributing watersheds of the Coal (OK121300010090_00) and Ranch (OK121300010060_00) Creeks.
There are 4 recorded no-discharge facilities in the Study Area. For the purposes of these TMDLs, no-discharge facilities do not contribute bacteria loading to the listed waterbodies and their tributaries. However, it is possible the wastewater collection systems associated with WWTPs could be a source of bacteria loading. While not all sewer overflows are reported, ODEQ has some data on sanitary sewer overflows (SSO) available.
There were a total of 923 SSO occurrences within the Study Area, ranging from 2 gallons (negligible amount) to > 8 million gallons between October 2004 and October 2009. The average reported release flow volume was 87,083 gallons during this five year period. Given the significant number of occurrences and the size of overflows reported, SSOs could be a significant source of bacteria loading to streams in the study area.
The City of Tulsa, located partially in the watershed, falls under requirements designated by USEPA for inclusion in the Phase I stormwater program. The small MS4 General Permit for communities in Oklahoma became effective on February 8, 2005. There are three cities and one county in the Study Area that fall under requirements designated by USEPA for inclusion in the Phase II Stormwater Program. These are (with their percent of watershed as MS4 in parentheses): Catoosa (2.5%), Owasso (7.8%), Broken Arrow (0.7%), and Tulsa County (3.4%). The Coal Creek watershed has two small areas that are part of Tulsa County’s MS4 responsibility (Figure 3-1b). The Ranch Creek watershed has City of Owasso and Tulsa County as its MS4 communities occupying a combined 32.5% of the area. There are no NPDES-permitted concentrated animal feeding operations (CAFOs) within the Study Area.
Within the Lower Bird Creek watershed, the three WWTP point sources are relatively minor contributors of bacteria and for the most part tend to meet instream water quality criteria in their effluent due to disinfection of effluent. Therefore, nonpoint sources and other point sources such as the municipal separate storm sewer systems (MS4s) areas in the watershed are considered to be the major origins of bacteria loading.
The four major nonpoint source categories contributing to the elevated bacteria in each of the watersheds in the Study Area are livestock, pets, deer, and septic tanks. Livestock and Lower Bird Creek Bacteria TMDLs Executive Summary
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domestic pets are estimated to be the largest contributors of fecal coliform loading to land surfaces. It must be noted that while no data are available to estimate populations and fecal loading of wildlife other than deer, a number of bacteria source tracking studies demonstrate that wild birds and mammals represent a major source of the fecal bacteria found in streams.
Nonpoint source bacteria loading to the receiving streams of each waterbody may emanate from a number of different sources including wildlife, various agricultural activities and domesticated animals, land application fields, urban runoff, failing onsite wastewater disposal systems, and domestic pets. The data analysis and the load duration curves (LDC) demonstrate that exceedances in stream segments are the result of a variety of nonpoint source loading occurring during a range of flow conditions.
E.3 Using Load Duration Curves to Develop TMDLs
The TMDL calculations presented in this report are derived from LDCs. LDCs facilitate rapid development of TMDLs and as a TMDL development tool, may assist in identifying whether impairments are associated with point or nonpoint sources.
Use of the LDC obviates the need to determine a design storm or selected flow recurrence interval with which to characterize the appropriate flow level for the assessment of critical conditions. For waterbodies impacted by both point and nonpoint sources, the “nonpoint source critical condition” would typically occur during high flows, when rainfall runoff would contribute the bulk of the pollutant load, while the “point source critical condition” would typically occur during low flows, when treatment plant effluents would dominate the base flow of the impaired water. However, flow range is only a general indicator of the relative proportion of point/nonpoint contributions. It is not used in this report to quantify point source or nonpoint source contributions. Violations that occur during low flows may not be caused exclusively by point sources. Violations have been noted in some watersheds that contain no point sources. Research has shown that bacteria loading in streams during low flow conditions may be due to wildlife in rural and urban areas (such as birds, raccoons, possums, etc.), pets and other domesticated animals, direct deposit of cattle manure into streams, and faulty septic tank/lateral field systems.
LDCs display the maximum allowable load over the complete range of flow conditions by a line using the calculation of flow multiplied by the water quality criterion. The TMDL can be expressed as a continuous function of flow, equal to the line, or as a discrete value derived from a specific flow condition.
The basic steps to generating an LDC involve: obtaining daily flow data for the site of interest from the U.S. Geological Survey ; sorting the flow data and calculating flow exceedance percentiles for the time period and season of interest; obtaining the water quality data from the primary contact recreation season (May 1 through September 30); matching the water quality observations with the flow data from the same date; display a curve on a plot that represents the allowable load determined by multiplying the actual or estimated flow by the WQS for each respective indicator; Lower Bird Creek Bacteria TMDLs Executive Summary
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multiplying the flow by the water quality parameter concentration to calculate daily loads; then plotting the flow exceedance percentiles and daily load observations in a load duration plot.
For bacteria TMDLs the culmination of these steps is expressed in the following formula, which is displayed on the LDC as the TMDL curve:
TMDL (cfu/day) = WQS * flow (cfs) * unit conversion factor
Where: WQS = 400 cfu /100 mL (Fecal coliform); 406 cfu/100 mL (E. coli); or 108 cfu/100 mL (Enterococci)
unit conversion factor = 24,465,525 mL*s / ft3*day
E.4 TMDL Calculations
As indicated above, the bacteria TMDLs for the 303(d)-listed waterbodies covered in this report were derived using LDCs. A TMDL is expressed as the sum of all WLAs (point source loads), LAs (nonpoint source loads), and an appropriate MOS, which attempts to account for lack of knowledge concerning the relationship between effluent limitations and water quality.
This definition can be expressed by the following equation:
TMDL = Σ WLA + Σ LA + MOS
The TMDLs presented in this report are expressed as a percent reduction across the full range of flow conditions (See Table ES-3). The difference between existing loading and the water quality target is used to calculate the loading reductions required.
Table ES-3 presents the percent reductions necessary for each bacterial indicator causing nonsupport of the PBCR use in the Study Area. For Fecal Coliform, the PRG is determined based on instantaneous criteria. For E. coli and Enterococci, the PRG will be the lesser of that required to meet the geometric mean or instantaneous criteria because WQS are considered to be met if, 1) either the geometric mean of all data is less than the geometric mean criteria, or 2) no samples exceed the instantaneous criteria. The appropriate PRG for each bacteria indicator for each waterbody in the study area is denoted by the bold text in Table ES-3. The PRGs range from 44.8 to 82.6 percent. Because the Coal and Ranch Creeks are tributaries to the Lower Bird Creek and because the load reduction goals for the Coal and Ranch Creeks are either equal or smaller than that for the Lower Bird Creek for E. Coli, the more restrictive load reduction goal of 44.8% for the Lower Bird Creek will apply to these two tributaries.
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Table ES-3 TMDL Percent Reductions Required to Meet Water Quality Standards for Impaired Waterbodies in the Study Area WQM Station Waterbody ID Waterbody Name Percent Reduction Required FC EC ENT Instant-aneous Instant-aneous Geo-mean Instant-aneous Geo-mean
OK121300010010-001AT
OK121300010010_00
Bird Creek (Lower)
64.1%
79.1%
44.8%
94.4%
82.6%
OK121300-01-0090M
OK121300010090_00
Coal Creek
44.8%†
58.6%
OK121300-01-0060G
OK121300010060_00
Ranch Creek
85.3%
32.8%†
† Because these two values are either equal or smaller than that for the Lower Bird Creek for E. Coli, the more restrictive load reduction goal of 44.8% for the Lower Bird Creek will apply to these two tributaries.
The TMDL, WLA, LA, and MOS vary with flow condition, and are calculated at every 5th flow interval percentile. For illustrative purposes, the TMDL, WLA, LA, and MOS are calculated for the median flow in Table ES-4. The WLA component of each TMDL is the sum of all WLAs within the contributing watershed of each waterbody. The sum of the WLAs can be represented as a single line below the LDC. The WLA for MS4s is estimated based on the percentage of MS4 area which falls within the study watershed. The LDC and the equation of:
Average LA = average TMDL - MOS - WLA_WWTF - WLA_MS4
can provide an individual value for the LA in counts per day, which represents the area under the TMDL target line and above the WLA line. For MS4s the load reduction will be the same as the PRG established for the overall watershed. Where there are no continuous point sources the WLA is zero.
Federal regulations (40 CFR §130.7(c)(1)) require that TMDLs include an MOS. The MOS is a conservative measure incorporated into the TMDL equation that accounts for lack of knowledge associated with calculating the allowable pollutant loading to ensure WQS are attained. USEPA guidance allows for use of implicit or explicit expressions of the MOS, or both. When conservative assumptions are used in development of the TMDL, or conservative factors are used in the calculations, the MOS is implicit. When a specific percentage of the TMDL is set aside to account for lack of knowledge, then the MOS is considered explicit. An explicit Margin of Safety of 10% was selected in this TMDL report.
E.5 Reasonable Assurance
As authorized by Section 402 of the CWA, ODEQ has delegation of the NPDES in Oklahoma, except for certain jurisdictional areas related to agriculture and the oil and gas industry retained by the Oklahoma Department of Agriculture and Oklahoma Corporation Commission, for which the USEPA has retained permitting authority. The NPDES program in Oklahoma is implemented via Title 252, Chapter 606 of the Oklahoma Pollutant Discharge Elimination System (OPDES) Act, and in accordance with the agreement between ODEQ and USEPA relating to administration and enforcement of the delegated NPDES program. Implementation of WLAs for point sources is done through permits issued under the OPDES program. Lower Bird Creek Bacteria TMDLs Executive Summary
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Table ES-4 TMDL Summaries Examples Waterbody ID WQM Station Waterbody Name Indicator Bacteria Species TMDL† (cfu/day) WLA_WWTP† (cfu/day) WLA_MS4 (cfu/day) LA† (cfu/day) MOS† (cfu/day)
OK121300010010_00
OK121300010010_001AT
Bird Creek (Lower)
ENT
8.11E+11
6.41E+10
4.41E+11
2.25E+11
8.11E+10
OK121300010090_00
OK121300-01-0090M
Coal Creek
EC
1.79E+10
0.00E+00
1.61E+10
0.00E+00
1.79E+09
OK121300010060_00
OK121300-01-0060G
Ranch Creek
EC
4.59E+10
0.00E+00
1.34E+10
2.79E+10
4.59E+09
† Derived for illustrative purposes at the median flow value Lower Bird Creek Bacteria TMDLs Introduction
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SECTION 1 INTRODUCTION
1.1 TMDL Program Background
Section 303(d) of the Clean Water Act (CWA) and U.S. Environmental Protection Agency (USEPA) Water Quality Planning and Management Regulations (40 Code of Federal Regulations [CFR] Part 130) require states to develop total maximum daily loads (TMDL) for waterbodies not meeting designated uses where technology-based controls are in place. TMDLs establish the allowable loadings of pollutants or other quantifiable parameters for a waterbody based on the relationship between pollution sources and in-stream water quality conditions, so states can implement water quality-based controls to reduce pollution from point and nonpoint sources and restore and maintain water quality (USEPA 1991).
This report documents the data and assessment used to establish TMDLs for the pathogen indicator bacteria fecal coliform, Escherichia coli (E. coli), and Enterococci for the waterbodies in the Study Area. Elevated levels of pathogen indicator bacteria in aquatic environments indicate that a receiving water is contaminated with human or animal feces and that there is a potential health risk for individuals exposed to the water. Data assessment and TMDL calculations are conducted in accordance with requirements of Section 303(d) of the CWA, Water Quality Planning and Management Regulations (40 CFR Part 130), USEPA guidance, and Oklahoma Department of Environmental Quality (ODEQ) guidance and procedures. ODEQ is required to submit all TMDLs to USEPA for review and approval. Once the USEPA approves a TMDL, then the waterbody may be moved to Category 4a of a state’s Integrated Water Quality Monitoring and Assessment Report, where it remains until compliance with water quality standards (WQS) is achieved (USEPA 2003).
The purpose of this TMDL report is to establish pollutant load allocations for indicator bacteria in impaired waterbodies, which is the first step toward restoring water quality and protecting public health. TMDLs determine the pollutant loading a waterbody can assimilate without exceeding the WQS for that pollutant. TMDLs also establish the pollutant load allocation necessary to meet the WQS established for a waterbody based on the relationship between pollutant sources and in-stream water quality conditions. A TMDL consists of a wasteload allocation (WLA), load allocation (LA), and a margin of safety (MOS). The WLA is the fraction of the total pollutant load apportioned to point sources, and includes stormwater discharges regulated under the National Pollutant Discharge Elimination System (NPDES) as point sources. The LA is the fraction of the total pollutant load apportioned to nonpoint sources. The MOS is a percentage of the TMDL set aside to account for the lack of knowledge associated with natural processes in aquatic systems, model assumptions, and data limitations.
This report does not stipulate specific control actions (regulatory controls) or management measures (voluntary best management practices) necessary to reduce bacteria loadings within the watershed. Watershed-specific control actions and management measures will be identified, selected, and implemented under a separate process involving stakeholders who live and work in the watershed, tribes, and local, state, and federal government agencies.
This TMDL report focuses on three waterbodies that ODEQ placed in Category 5a of the 2008 Integrated Report [303(d) list] for nonsupport of primary body contact recreation (PBCR): Lower Bird Creek Bacteria TMDLs Introduction
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Lower Bird Creek (OK121300010010_00), Coal Creek (OK121300010090_00), and Ranch Creek (OK121300010060_00).
Figures 1-1a and 1-1b are the location maps showing the impaired segments of the waterbodies and their contributing watersheds. The maps also display the locations of the water quality monitoring (WQM) station used as the basis for placement of the waterbodies on the Oklahoma 303(d) list and other related information. The waterbodies and the surrounding watersheds are hereinafter referred to as the Study Area. The Study Area, which is comprised of the watershed for all of Lower Bird Creek, also includes the two sub-watersheds of Coal Creek and Ranch Creek (Figure 1-1b) that are also impaired for bacteria. Both of these segments are listed in the 2008 303(d) list as impaired for E. coli. The TMDL load reductions calculated for the entire Lower Bird Creek watershed will apply to them as well. Separate TMDLs for the two tributaries are also prepared in this report. The more restrictive TMDL reduction goals will apply to these two tributaries.
Elevated levels of bacteria above the WQS result in the requirement that a TMDL be developed. The TMDLs established in this report are a necessary step in the process to develop the bacteria loading controls needed to restore the contact recreation use designated for each waterbody. Table 1-1 provides a description of the locations of the WQM stations on the 303(d)-listed waterbodies.
Table 1-1 Water Quality Monitoring Stations used for 2008 303(d) Listing Decision Waterbody Name Waterbody ID WQM Station WQM Station Location Descriptions
Bird Creek (Lower)
OK121300010010_00
OK121300010010-001AT
Bird Creek, Hwy 266 bridge
Coal Creek
OK121300010090_00
OK121300-01-0090M
Coal Creek: Hwy 11
Ranch Creek
OK121300010060_00
OK121300-01-0060G
Ranch Creek: Owasso
1.2 Watershed Description
General. The watershed of Lower Bird Creek addressed in these TMDLs is located in northeast Oklahoma. The waterbodies addressed in this report are located in portions of Tulsa, Osage and Rogers Counties.
Within the Level IV ecoregion classification, nearly all of the study area falls into the Central Irregular Plains ecoregion. The Central Oklahoma/Texas Plains ecoregion is on the western tip of the watershed.
Table 1-2, derived from the 2000 U.S. Census, demonstrates that with the exception of the metropolitan City of Tulsa portion of the watershed in Tulsa County, the remainder of the study area is mostly sparsely populated (U.S. Census Bureau 2000).
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Table 1-2 County Population and Density County Name Population (2000 Census) Population Density (per square mile)
Tulsa
563,303
988.2
Osage
44,433
19.7
Rogers
70,640
104.7
Climate. Table 1-3 summarizes the average annual precipitation for the Lower Bird Creek watershed. The annual precipitation within the watershed in this portion of Oklahoma ranges between 39.8 (Osage County) and 44.0 (Rogers County) inches, increasing from the west to east (Oklahoma Climatological Survey, 2005).
Table 1-3 Average Annual Precipitation by Watershed Study Area Precipitation Summary Waterbody Name Waterbody ID Average Annual (Inches)
Bird Creek (Lower)
OK121300010010_00
41.9
Coal Creek
OK121300010090_00
41.9
Ranch Creek
OK121300010060_00
41.9
Land Use. Table 1-4 summarizes the acreages and the corresponding percentages of the land use categories for the contributing watersheds associated with the waterbodies in the Study Area. The land use/land cover data were derived from the U.S. Geological Survey (USGS) 2001 National Land Cover Dataset (USGS 2007). The land use categories are displayed in Figure 1-2.
In the Lower Bird Creek watershed, the largest percentage land use category (20.2%) is for Developed Low Density. Several mostly rural land use categories (around 13% to 16% each) are the next dominant: Developed Open Space, Deciduous Forest, Grasslands/Herbaceous, and Pasture/Hay. Combined, these mostly vegetative land uses comprise nearly two-thirds (59.9%) of the watershed. Developed High Density is another 7.5% of the watershed, with the remaining categories under 2% each or not present.
Coal Creek is mostly an urban watershed with 67% of the land classified as developed. Ranch Creek, on the other hand, is mostly a rural watershed with forest, grassland, and pasture accounting for 75% of the total watershed area.
The City of Tulsa lies within 51.8% of the Lower Bird Creek watershed. Owasso is 7.8 % of the watershed, Catoosa 2.5%, and Broken Arrow 0.7%. The rest is unincorporated county land. All of these cities are Phase II stormwater permitted cities except Tulsa which has a Phase I permit. Tulsa County also has a Phase II stormwater permit, and its permitted Urbanized Area occupies 3.4% of the Lower Bird Creek watershed. Together, about two-thirds (66.2%) of the watershed is made up of stormwater permitted areas. The Coal Creek watershed Lower Bird Creek Bacteria TMDLs Introduction
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lies almost entirely within the City of Tulsa while about one third of the Ranch Creek watershed is within the City of Owasso.
Figure 1-1a Watersheds Not Supporting Primary Body Contact Recreation Use within the Study Area
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Figure 1-1b Coal and Ranch Creek Watersheds
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Table 1-4 Land Use Summaries by Watershed Grid Code Category Description Bird Creek (Lower) Coal Creek Ranch Creek Acres Percent Acres Percent Acres Percent
11
Open Water
3832.7
3.3
1621.1
14.2
388.4
3.1
21
Developed, Open Space
17,456.6
15.2
2,002.5
19.0
1,267.5
10.2
22
Developed, Low Density
22,689.3
19.7
0
0
0
0
23
Developed, Medium Density
10,716.4
9.3
3,876.9
36.9
1,003.7
8.1
24
Developed, High Density
8,386.9
7.3
1,164.7
11.1
105.0
0.9
31
Barren Land (Rock/Sand/Clay)
69.1
0.1
0
0
0
0
41
Deciduous Forest
14,736.7
12.8
1,129.1
10.7
2,367.9
19.1
42
Evergreen Forest
25.0
0.0
0
0
3.1
0.03
71
Grassland / Herbaceous
17,251.2
15.0
541.3
5.2
2,899.6
23.4
81
Pasture / Hay
17,834.6
15.5
179.5
1.7
4,009.0
32.4
82
Cultivated Crops
1,923.9
1.7
0
0
326.9
2.6
90
Woody Wetlands
1.9
0.002
2.0
0.02
0
0
95
Emergent Herbaceous Wetlands
0.2
0.0
0
0
2.2
0.02
TOTAL:
114,924
100
10,517
100
12,373
100
Data Source: USGS 2001 National Land Cover Database Zone 32 Land Cover Layer developed by the Multi-Resolution Land Characteristics (MRLC) Consortium.
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Figure 1-2 Land Use Map by Watershed Lower Bird Bacteria TMDLs Problem Identification and Water Quality Target
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SECTION 2 PROBLEM IDENTIFICATION AND WATER QUALITY TARGET
2.1 Oklahoma Water Quality Standards
Title 785 of the Oklahoma Administrative Code includes Oklahoma’s water quality standards (OWRB 2008a). The OWRB has statutory authority and responsibility concerning establishment of state water quality standards, as provided under 82 Oklahoma Statute [O.S.], §1085.30. This statute authorizes the OWRB to promulgate rules …which establish classifications of uses of waters of the state, criteria to maintain and protect such classifications, and other standards or policies pertaining to the quality of such waters. [O.S. 82:1085:30(A)]. Beneficial uses are designated for all waters of the state. Such uses are protected through restrictions imposed by the antidegradation policy statement, narrative water quality criteria, and numerical criteria (OWRB 2008a). Table 2-1a, an excerpt from the 2008 Integrated Report (ODEQ 2008), lists beneficial uses designated for each impaired stream segment in this TMDL. The TMDLs in this report only address the PBCR-designated use.
Tables 2-1a and b, excerpts from Appendix C of the 2008 Integrated Report (ODEQ 2008), summarize the beneficial uses attainment status for the waterbodies in the Study Area and targeted TMDL dates. The priority for targeting TMDL development and implementation is derived from the chronological order of the dates listed in the TMDL Date column of Table 2-1a. The TMDLs established in this report are a necessary step in the process to restore the PBCR use designation for each waterbody.
Table 2-1a Excerpt from the 2008 Integrated Report – Comprehensive Waterbody Assessment Category List Waterbody ID Waterbody Name Stream Miles Category Priority TMDL Date Fecal Coliform E.coli Enterococci Primary Body Contact Recreation
OK121300010010_00
Bird Creek (Lower)
23.8
5a
1
2010
X
X
X
N
OK121300010090_00
Coal Creek
6.71
5a
1
2010
X
N
OK121300010060_00
Ranch Creek
6.94
5a
1
2010
X
N
N = Not Supporting; Source: 2008 Integrated Report, ODEQ 2008
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Table 2-1b Designated Beneficial Uses for Each Impaired Streams in the Study Area* Waterbody ID Waterbody Name AES AG WWAC FISH PBCR PPWS
OK121300010010_00
Bird Creek (Lower)
I
N
N
F
N
N
OK121300010090_00
Coal Creek
I
I
I
X
N
OK121300010060_00
Ranch Creek
I
I
X
N
* I: Insufficient information; N: Not supporting; F: Fully supporting; X: not assessed.
The definition of PBCR is summarized by the following excerpt from Chapter 45 of the Oklahoma WQS.
(a) Primary Body Contact Recreation involves direct body contact with the water where a possibility of ingestion exists. In these cases the water shall not contain chemical, physical or biological substances in concentrations that are irritating to skin or sense organs or are toxic or cause illness upon ingestion by human beings.
(b) In waters designated for Primary Body Contact Recreation...limits...shall apply only during the recreation period of May 1 to September 30. The criteria for Secondary Body Contact Recreation will apply during the remainder of the year.
To implement Oklahoma’s WQS for PBCR, OWRB promulgated Chapter 46, Implementation of Oklahoma’s Water Quality Standards (OWRB 2008b). The excerpt below from Chapter 46: 785:46-15-6, stipulates how water quality data will be assessed to determine support of the PBCR use as well as how the water quality target for TMDLs will be defined for each bacteria indicator.
(a) Scope. The provisions of this Section shall be used to determine whether the subcategory of Primary Body Contact of the beneficial use of Recreation designated in OAC 785:45 for a waterbody is supported during the recreation season from May 1 through September 30 each year. Where data exist for multiple bacterial indicators on the same waterbody or waterbody segment, the determination of use support shall be based upon the use and application of all applicable tests and data.
(b) Screening levels.
(1) The screening level for fecal coliform shall be a density of 400 colonies per 100ml.
(2) The screening level for Escherichia coli shall be a density of 235 colonies per 100 ml in streams designated in OAC 785:45 as Scenic Rivers and in lakes, and 406 colonies per 100 ml in all other waters of the state designated as Primary Body Contact Recreation.
(3) The screening level for Enterococci shall be a density of 61 colonies per 100 ml in streams designated in OAC 785:45 as Scenic Rivers and in lakes, and 108 colonies per 100 ml in all other waters of the state designated as Primary Body Contact Recreation. Lower Bird Bacteria TMDLs Problem Identification and Water Quality Target
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(c) Fecal coliform:
(1) The Primary Body Contact Recreation subcategory designated for a waterbody shall be deemed to be fully supported with respect to fecal coliform if the geometric mean of 400 colonies per 100 ml is met and no greater than 25% of the sample concentrations from that waterbody exceed the screening level prescribed in (b) of this Section.
(2) The parameter of fecal coliform is not susceptible to an assessment that Primary Body Contact Recreation is partially supported.
(3) The Primary Body Contact Recreation subcategory designated for a waterbody shall be deemed to be not supported with respect to fecal coliform if the geometric mean of 400 colonies per 100 ml is not met, or greater than 25% of the sample concentrations from that waterbody exceed the screening level prescribed in (b) of this Section, or both such conditions exist.
(d) Escherichia coli (E. coli):
(1) The Primary Body Contact Recreation subcategory designated for a waterbody shall be deemed to be fully supported with respect to E. coli if the geometric mean of 126 colonies per 100 ml is met, or the sample concentrations from that waterbody taken during the recreation season do not exceed the screening level prescribed in (b) of this Section, or both such conditions exist.
(2) The parameter of E. coli is not susceptible to an assessment that Primary Body Contact Recreation is partially supported.
(3) The Primary Body Contact Recreation subcategory designated for a waterbody shall be deemed to be not supported with respect to E. coli if the geometric mean of 126 colonies per 100 ml is not met and any of the sample concentrations from that waterbody taken during the recreation season exceed a screening level prescribed in (b) of this Section.
(e) Enterococci:
(1) The Primary Body Contact Recreation subcategory designated for a waterbody shall be deemed to be fully supported with respect to Enterococci if the geometric mean of 33 colonies per 100 ml is met, or the sample concentrations from that waterbody taken during the recreation season do not exceed the screening level prescribed in (b) of this Section, or both such conditions exist.
(2) The parameter of Enterococci is not susceptible to an assessment that Primary Body Contact Recreation is partially supported.
(3) The Primary Body Contact Recreation subcategory designated for a waterbody shall be deemed to be not supported with respect to Enterococci if the geometric mean of 33 colonies per 100 ml is not met and any of the sample concentrations from that waterbody taken during the recreation season exceed a screening level prescribed in (b) of this Section.
Compliance with the Oklahoma WQS is based on meeting requirements for all three bacteria indicators. Where concurrent data exist for multiple bacterial indicators on the same waterbody or waterbody segment, each indicator group must demonstrate compliance with the numeric criteria prescribed (OWRB 2008a). Lower Bird Bacteria TMDLs Problem Identification and Water Quality Target
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As stipulated in the WQS, utilization of the geometric mean to determine compliance for any of the three indicator bacteria depends on the collection of five samples within a 30-day period. For most stream segments in Oklahoma there are insufficient data available to calculate the 30-day geometric mean since most water quality samples are collected once a month. As a result, waterbodies placed on the 303(d) list for not supporting the PBCR are the result of individual samples exceeding the instantaneous criteria or the long-term geometric mean of individual samples exceeding the geometric mean criteria for each respective bacteria indicator. Targeting the instantaneous criterion established for the primary contact recreation season (May 1st to September 30th) as the water quality goal for TMDLs corresponds to the basis for 303(d) listing and may be protective of the geometric mean criterion as well as the criteria for the secondary contact recreation season. However, both the instantaneous and geometric mean criteria for E. coli and Enterococci will be evaluated as water quality targets to ensure the most protective goal is established for each waterbody.
The specific data assessment method for listing indicator bacteria based on instantaneous or single sample criterion is detailed in Oklahoma’s 2008 Integrated Report. As stated in the report, a minimum of 10 samples collected between May 1st and September 30th (during the primary recreation season) is required to list a segment for E. coli and Enterococci. In addition only data that were collected from the most recent five primary recreation seasons are used in attainment assessment and TMDL calculations. In case that there are less than 10 primary recreation season samples available from the five seasons, one more season is backtracked to add more samples. This process is repeated until 10 samples are obtained or no more data are available.
A sample quantity exception exists for fecal coliform that allows waterbodies to be listed for nonsupport of PBCR if there are less than 10 samples. The assessment method states that if there are less than 10 samples and the existing sample set already assures a nonsupport determination, then the waterbody should be listed for TMDL development. This condition is true in any case where the small sample set demonstrates that at least three out of six samples exceed the single sample fecal coliform criterion. In this case if four more samples were available to meet minimum of 10 samples, this would still translate to >25 percent exceedance or nonsupport of PBCR (i.e., three out of 10 samples = 33 percent exceedance). For E. coli and Enterococci, the 10-sample minimum was used, without exception, in attainment determination.
2.2 Problem Identification
Table 2-2 summarizes water quality data collected during the primary contact recreation season from the stream segments for the most recent 5 years (or the number of years where a total of at least 10 samples were collected) for each indicator bacteria. Water quality data from the primary contact recreation seasons used in this TMDL assessment are provided in Appendix A. The data from three separate monitoring programs were used in this TMDL study. The OWRB’s BUMP site at Highway 266 crossing (OK121300010010_001AT) had data for the recreational season for all three bacteria indicators for the Lower Bird Creek, but for only the 2006 season. Therefore, fecal coliform data collected by City of Tulsa at a stream monitoring site (Site BC-5b) approximately 1.5 miles upstream of the BUMP site were also used. The Tulsa site had data for the recreational season for only fecal coliform, but for a five year period of 2005 through July 2009. The fecal coliform data from both the OWRB and City Lower Bird Bacteria TMDLs Problem Identification and Water Quality Target
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Table 2-2 Summary of Indicator Bacteria Samples from Primary Contact Recreation Season, 2003-2009* Waterbody ID Waterbody Name Indicator Bacteria Single Sample Water Quality Criterion (#/100ml) Geometric Mean Concentration (count/100ml) Number of Samples Number of Samples Exceeding Single Sample Criterion % of Samples Exceeding Single Sample Criterion Reason for Listing Change**
OK121300010010_00
Bird Creek (Lower) FC
400
367
54
23
43%
No change, TMDL needed EC
406
205
10
4
40%
No change, TMDL needed ENT
108
170
10
5
50%
No change, TMDL needed
OK121300010090_00
Coal EC
406
271
10
4
40%
No change, TMDL needed
OK121300010060_00
Ranch EC
406
167
13
4
31%
No change, TMDL needed
EC = E. coli; ENT = Enterococci; FC = fecal coliform. *2005-2009 for Bird Creek (Lower).
**Highlighted bacteria indicators require TMDL.
Table 2-3 Waterbodies Requiring TMDLs for Not Supporting Primary Contact Recreation Use WQM Station Waterbody ID Waterbody Name Indicator Bacteria FC E. coli ENT
OK121300010010-001AT
OK121300010010_00
Bird Creek (Lower)
X
X
X
OK121300-01-0090M
OK121300010090_00
Coal Creek
X
OK121300-01-0060G
OK121300010060_00
Ranch Creek
X
ENT = Enterococci; FC = fecal coliform
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of Tulsa sites were combined as indicated in Appendix A. For the data collected between 2005 and 2009, evidence of nonsupport of the PBCR use was based on all three bacteria indicators (fecal coliform, E. coli and Enterococcus) observed in the Lower Bird Creek (OK121300010010_00) segment. E. Coil data collected by the Oklahoma Conservation Commission (OCC) on the Coal (OK121300010090_00) and Ranch (OK121300010060_00) Creeks showed nonsupport of the PBCR use for both creeks. Table 2-3 summarizes the TMDLs required for the waterbodies for not supporting PBCR.
2.3 Water Quality Target
The Code of Federal Regulations (40 CFR §130.7(c)(1)) states that, “TMDLs shall be established at levels necessary to attain and maintain the applicable narrative and numerical water quality standards.” For the waterbodies requiring TMDLs in this report, defining the water quality target is somewhat complicated by the use of three different bacteria indicators with three different numeric criteria for determining attainment of PBCR use as defined in the Oklahoma WQS. As previously stated, because available bacteria data were collected on an approximate monthly basis (see Appendix A) instead of at least five samples over a 30–day period, data for these TMDLs are analyzed and presented in relation to the instantaneous criteria for fecal coliform and both the instantaneous and a long-term geometric mean for both E. coli and Enterococci.
All TMDLs for fecal coliform must take into account that no more than 25 percent of the samples may exceed the instantaneous numeric criteria. For E. coli and Enterococci, no samples may exceed instantaneous criteria. Since the attainability of stream beneficial uses for E. coli and Enterococci is based on the compliance of either the instantaneous or a long-term geometric mean criterion, percent reductions goals will be calculated for both criteria. TMDLs will be based on the percent reduction required to meet either the instantaneous or long-term geometric mean criterion, whichever is less.
The water quality target for the waterbody will also incorporate an explicit 10 percent MOS. For example, if fecal coliform is utilized to establish the TMDL, then the water quality target is 360 organisms per 100 milliliters (mL), 10 percent lower than the instantaneous water quality criteria (400/100 mL). For E. coli the instantaneous water quality target is 365 organisms/100 mL, which is 10 percent lower than the criterion value (406/100 mL), and the geometric mean water quality target is 113 organisms/100 mL, which is 10 percent lower than the criterion value (126/100 mL). For Enterococci the instantaneous water quality target is 97/100 mL, which is 10 percent lower than the criterion value (108/100 mL) and the geometric mean water quality target is 30 organisms/100 mL, which is 10 percent lower than the criterion value (33/100 mL).
Each water quality target will be used to determine the allowable bacteria load which is derived by using the actual or estimated flow record multiplied by the in-stream criteria minus a 10 percent MOS.
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SECTION 3 POLLUTANT SOURCE ASSESSMENT
A source assessment characterizes known and suspected sources of pollutant loading to impaired waterbodies. Sources within a watershed are categorized and quantified to the extent that information is available. Bacteria originate from humans and warm-blooded animals. Sources may be point or nonpoint in nature.
Point sources are permitted through the NPDES program. NPDES-permitted facilities that discharge treated wastewater are required to monitor for one of the three bacteria indicators (fecal coliform, E coli, or Enterococci) in accordance with its permit. Nonpoint sources are diffuse sources that typically cannot be identified as entering a waterbody through a discrete conveyance at a single location. These sources may involve land activities that contribute bacteria to surface water as a result of rainfall runoff. For the TMDLs in this report, all sources of pollutant loading not regulated by NPDES are considered nonpoint sources. The following discussion describes what is known regarding point and nonpoint sources of bacteria in the impaired watersheds.
3.1 NPDES-Permitted Facilities
Under 40CFR, §122.2, a point source is described as a discernable, confined, and discrete conveyance from which pollutants are or may be discharged to surface waters. Certain NPDES-permitted municipal plants are classified as no-discharge facilities. NPDES-permitted facilities classified as point sources that may contribute bacteria loading include: NPDES municipal wastewater treatment plants (WWTP); NPDES municipal no-discharge WWTP; NPDES municipal separate storm sewer discharge (MS4); and NPDES Concentrated Animal Feeding Operation (CAFO).
Continuous point source discharges such as WWTPs, could result in discharge of elevated concentrations of fecal coliform bacteria if the disinfection unit is not properly maintained, is of poor design, or if flow rates are above the disinfection capacity. While the no-discharge facilities do not discharge wastewater directly to a waterbody, it is possible that the collection systems associated with each facility may be a source of bacteria loading to surface waters. Stormwater runoff from MS4 areas, which is now regulated under the USEPA NPDES Program, can also contain high bacteria concentrations. CAFOs are recognized by USEPA as significant sources of pollution, and may have the potential to cause serious impacts to water quality if not properly managed.
There are three continuous municipal WWTP point source dischargers and 16 industrial point source dischargers in the Study Area. There also is one MS4 Phase I stormwater permitted city and five Phase II MS4 permittees in the watershed. The MS4 permitted areas are also shown in Figures 3-1a and 3-1b.
3.1.1 Continuous Point Source Discharges
The locations of the NPDES-permitted facilities which discharge wastewater to surface waters addressed in these TMDLs are shown in Figure 3-1 and listed in Table 3-1. For the purposes of the pollutant source assessment only facility types identified in Table 3-1 as Lower Bird Bacteria TMDLs Pollutant Source Assessment
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Municipal are assumed to contribute bacteria loads within the watershed of Lower Bird Creek. For the industrial facilities in Table 3-1 the design flow was not available (N/A).
Figure 3-1a Locations of NPDES-Permitted Facilities and MS4s in the Bird Creek (Lower) Watershed
Lower Bird Bacteria TMDLs Pollutant Source Assessment
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Figure 3-1b MS4s in the Coal and Ranch Creek Watersheds
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Table 3-1 Point Source Discharges in the Study Area NPDES Permit No. Name Receiving Water Facility Type County Name Design Flow (mgd) Active/ Inactive Facility ID
OK0020303
Owasso Public Works Auth.
Unnamed tributary to Bird Creek
Municipal
Tulsa
3.3
Active
S21310
OK0026221
Tulsa MUA Northside
OK121300010010_00 Bird Creek
Municipal
Tulsa
42.6
Active
S21309
OK0042935
Tulsa MUA Lower Bird Cr Regional
OK121300010010_00 Bird Creek
Municipal
Tulsa
5.41
Active
S21327
OK0043001
APAC-Oklahoma, Inc. Tulsa Qur.
Bird Creek watershed
Industrial
Tulsa
N/A
Active
720000520
OKG110042
Mid-Continent Concrete Co-Mng
Bird Creek watershed
Industrial
Tulsa
N/A
Active
72002310
OK0040801
Anchor Stone Co. Tulsa Rock
Elm Creek watershed
Industrial
Tulsa
N/A
Active
66001140
OK0001210
Longview Lake Homeowners Assn.
Mingo Creek watershed
Industrial
Tulsa
N/A
Active
72002710
OK0001554
Spirit Aerosystems, Inc.
Mingo Creek watershed
Industrial
Tulsa
N/A
Active
72000630
OK0031844
Tulsa International Airport
Coal and Mingo Creek watersheds
Industrial
Tulsa
N/A
Active
72001420
OK0035351
Darr Equipment Co, Tulsa
Mingo Creek watershed
Industrial
Tulsa
N/A
Active
72001270
OK0042374
US Army Aviation Support Fac.
Mingo Creek watershed
Industrial
Tulsa
N/A
Active
72002280
OK0044130
Anchor Stone Co. 36th Street
Mingo Creek watershed
Industrial
Tulsa
N/A
Active
72002430
OKG110046
Rainbow Concrete Tulsa Plant
Mingo Creek watershed
Industrial
Tulsa
N/A
Active
72001700
OK0040789
LaFarge Building Materials, Inc.
Knudson Creek watershed
Industrial
Tulsa
N/A
Active
66001770
OK0042447
Expo Water Park Inc. D/B/A/ Big
Mill Creek watershed
Industrial
Tulsa
N/A
Active
72001900
OK0040711
International American Ceramic
Ranch Creek watershed
Industrial
Tulsa
N/A
Active
72002040
OK0040819
OK National Guard, Tulsa IAP
Coal Creek watershed
Industrial
Tulsa
N/A
Active
72002020 Lower Bird Bacteria TMDLs Pollutant Source Assessment
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NPDES Permit No. Name Receiving Water Facility Type County Name Design Flow (mgd) Active/ Inactive Facility ID
OK0026166
Tulsa MUA Mohawk Water Plant
Flat Rock Creek watershed
Industrial
Tulsa
N/A
Active
W21601
OK0038695
Facet International, Inc.
Flat Rock Creek watershed
Industrial
Tulsa
N/A
Active
72000400
N/A = not available
Discharge Monitoring Report (DMR) data was used to determine the number of fecal coliform analyses performed from 1999 through 2009, the maximum concentration during this period, and the number of violations when a daily maximum concentration exceeded 400 cfu/100 mL. DMR data was for fecal coliform only (see Appendix B). These data indicate that there were no geometric mean violations occurring at any of the three municipal WWTPs, and only one WWTP (Lower Bird Creek Regional) had any violations (3) of the maximum concentration occurring during the reporting period in Appendix B.
3.1.2 No-Discharge Facilities and SSOs
There are four recorded no-discharge facilities in the Study Area. For the purposes of these TMDLs, no-discharge facilities do not contribute bacteria loading to the Lower Bird Creek and its tributaries. However, it is possible the wastewater collection systems associated with those WWTPs could be a source of bacteria loading, or that discharges may occur during large rainfall events that exceed the systems’ storage capacities.
Table 3-2 NPDES No-Discharge Facilities in the Study Area Facility Facility ID County Facility Type Type Watershed
LEWIS TRAVEL TRAILERS
S21319
Tulsa
Total Retention
Industrial
Lower Bird Creek
OK121300010010_00
RAINBOW CONCRETE COMPANY
N/A
Tulsa
Total Retention
Industrial
Lower Bird Creek
OK121300010010_00
TWIN CITIES READY MIX, IN
N/A
Tulsa
Total Retention
Industrial
Lower Bird Creek
OK121300010010_00
QUARRY RECYCLING & DISPOS
N/A
Tulsa
Total Retention
Industrial
Lower Bird Creek
OK121300010010_00
N/A = not available
Sanitary sewer overflows (SSO) from wastewater collection systems, although infrequent, can be a major source of fecal coliform loading to streams. SSOs have existed since the introduction of separate sanitary sewers, and most are caused by blockage of sewer pipes by grease, tree roots, and other debris that clog sewer lines, by sewer line breaks and leaks, cross Lower Bird Bacteria TMDLs Pollutant Source Assessment
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connections with storm sewers, and inflow and infiltration of groundwater into sanitary sewers. SSOs are permit violations that must be addressed by the responsible NPDES permittee. The reporting of SSOs has been strongly encouraged by USEPA, primarily through enforcement and fines. While not all sewer overflows are reported, ODEQ has some data on SSOs available. There were a total of 923 SSO occurrences within the Lower Bird Creek watershed, ranging from 2 gallons (negligible amount) to > 8 million gallons between October 2004 and October 2009. The average reported release flow volume was 87,083 gallons during this five year period. SSO data are summarized in Table 3-3. Additional data on each individual SSO event are provided in Appendix B. Given the significant number of occurrences and the size of overflows reported, bacteria from SSOs could have been a significant source of bacteria loading in the past in the Lower Bird Creek watershed.
Table 3-3 Sanitary Sewer Overflow Summary Facility Name NPDES Permit No. Receiving Water Facility ID Number of Occurrences Date Range Amount (Gallons) From To Min Max
Owasso
OK0020303
Unnamed tributary to Bird Creek
S21310
158
10/1/2004
9/30/2009
2
>1,000,000
Lower Bird Creek Regional
OK0042935
OK121300010010_00 Bird Creek
S21327
1
2/1/2006
2/1/2006
510
510
Tulsa Northside
OK0026221
OK121300010010_00 Bird Creek
S21309
764
9/18/2004
9/28/2009
6
>8,000,000
SSOs are a common result of the aging wastewater infrastructure around the state. Due to the widespread nature of the SSO problem, DEQ has focused on first targeting SSOs that result in definitive environmental harm, such as fish kills, or lead to citizen complaints. All SSOs falling in these two categories are addressed through DEQ’s formal enforcement process. A Notice of Violation (NOV) is first issued to the owner of the collection system and a Consent Order (CO) is negotiated between the owner and DEQ to establish a schedule for necessary collection system upgrades to eliminate future SSOs.
Another target area for DEQ is chronic SSOs from OPDES major facilities, those with a total design flow in excess of 1 MGD. DEQ periodically reviews the bypass reports submitted by these major facilities and identifies problem areas and chronic SSOs. When these problems are attributable to wet weather, DEQ normally enters into a CO with the owner of the collection system to establish a schedule for necessary repairs. When the problems seem to be dry weather-related, DEQ will encourage the owner of the collection system to implement the proposed Capacity, Management, Operation, and Maintenance (CMOM) guidelines aimed at minimizing or eliminating dry weather SSOs. This is often accomplished through entering into a Consent Order to establish a schedule for implementation and annual auditing of the CMOM program.
All SSOs are considered unpermitted discharges under State statute and DEQ regulations. The smaller towns have a smaller reserve, are more likely to use utility revenue for general purposes, and/or tend to budget less for ongoing and/or preventive maintenance. If and when DEQ becomes aware of chronic SSOs (more than one from a single location in a year) or receives a complaint about an SSO in a smaller community, DEQ will pursue enforcement Lower Bird Bacteria TMDLs Pollutant Source Assessment
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action. Enforcement almost always begins with the issuance of an NOV and, if the problem is not corrected by a long-term solution, DEQ will enter into a CO with the facility for a long-term solution. Long-term solutions usually begin with sanitary sewer evaluation surveys (SSESs). Based on the result of the SSES, the facilities can prioritize and take corrective action.
3.1.3 NPDES Municipal Separate Storm Sewer Discharge (MS4)
Phase I MS4
In 1990 the USEPA developed rules establishing Phase I of the NPDES Stormwater Program, designed to prevent harmful pollutants from being washed by stormwater runoff into MS4s (or from being dumped directly into the MS4) and then discharged into local water bodies (USEPA 2005). Phase I of the program required operators of medium and large MS4s (those generally serving populations of 100,000 or greater) to implement a stormwater management program as a means to control polluted discharges. Approved stormwater management programs for medium and large MS4s are required to address a variety of water quality-related issues, including roadway runoff management, municipal-owned operations, and hazardous waste treatment. There is one Phase I MS4 permit in the Study Area: the City of Tulsa (NPDES permit No: OKS000201). The corporate limits constituting Tulsa’s permitted MS4 area occupies 51.8% (59,527 acres) of the Lower Bird Creek watershed. The Coal Creek watershed lies entirely within Tulsa’s corporate limits. Only a sliver of the Ranch Creek watershed is part of the City of Tulsa. The MS4 areas are shown in Figures 3-1a and 3-1b.
Phase II MS4s
Phase II of the rules developed by the USEPA extends coverage of the NPDES Stormwater Program to certain small MS4s. Small MS4s are defined as any MS4 that is not a medium or large MS4 covered by Phase I of the NPDES Stormwater Program. Phase II requires operators of regulated small MS4s to obtain NPDES permits and develop a stormwater management program. These programs are designed to reduce discharges of pollutants to the “maximum extent practicable,” protect water quality, and satisfy appropriate water quality requirements of the CWA. Because stormwater discharges cannot be centrally collected, monitored, and treated, they are not subject to the same types of effluent limitations as wastewater facilities. Instead, stormwater discharges are required to meet a performance standard of providing treatment to the “maximum extent practicable” (MEP) through the implementation of best management practices (BMPs).
Small MS4 stormwater programs must address the following minimum control measures: Public Education and Outreach; Public Participation/Involvement; Illicit Discharge Detection and Elimination; Construction Site Runoff Control; Post- Construction Runoff Control; and Pollution Prevention/Good Housekeeping.
The small MS4 General Permit for communities in Oklahoma became effective on February 8, 2005. There are three cities and one county in the Study Area that fall under requirements designated by USEPA for inclusion in the Phase II Stormwater Program. These Lower Bird Bacteria TMDLs Pollutant Source Assessment
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are (with their percent of watershed as MS4 and NPDES permit numbers in parentheses): Catoosa (2.5%, OKR040033), Owasso (7.8%, OKR040029), Broken Arrow (0.7%, OKR040001), and Tulsa County (3.4%, OKR040019). The Coal Creek watershed has two small areas that are part of Tulsa County’s MS4 responsibility (Figure 3-1b). The Ranch Creek watershed has City of Owasso and Tulsa County as its MS4 communities occupying a combined 32.5% of the area (Figure 3-1b).
ODEQ provides information on the current status of their MS4 programs on its website found at: http://www.deq.state.ok.us/WQDnew/stormwater/ms4/
3.1.4 Concentrated Animal Feeding Operations
The Agricultural Environmental Management Services (AEMS) of the Oklahoma Department of Agriculture, Food and Forestry (ODAFF) was created to help develop, coordinate, and oversee environmental policies and programs aimed at protecting the Oklahoma environment from pollutants associated with agricultural animals and their waste. Through regulations established by the Oklahoma Concentrated Animal Feeding Operation Act, AEMS works with producers and concerned citizens to ensure that animal waste does not impact the waters of the state. A CAFO is an animal feeding operation that confines and feeds at least 1,000 animal units for 45 days or more in a 12-month period (ODAFF 2005). The CAFO Act is designed to protect water quality through the use of best management practices (BMP) such as dikes, berms, terraces, ditches, or other similar structures used to isolate animal waste from outside surface drainage, except for a 25-year, 24–hour rainfall event (ODAFF 2005). CAFOs are considered no-discharge facilities.
CAFOs are designated by USEPA as significant sources of pollution, and may have the potential to cause serious impacts to water quality if not managed properly. Potential problems for CAFOs can include animal waste discharges to waters of the state and failure to properly operate wastewater lagoons.
Regulated CAFOs operate under NPDES permits issued and overseen by EPA. In order to comply with this TMDL, any CAFO permits in the watershed and their associated management plans must be reviewed. Further actions to reduce bacteria loads and achieve progress toward meeting the specified reduction goals must be implemented. This provision will be forwarded to EPA and ODAFF for follow-up. However, the Lower Bird Creek watershed has no permitted CAFO operations. Table 3-4 specifies that there are no CAFOs located in the Study Area.
Table 3-4 NPDES-Permitted CAFOs in Study Area ODAFF Owner ID EPA Facility ODAFF ID ODAFF License Number Maximum Number of Permitted Animals at Facility Total # of Animal Units at Facility County Watershed Dairy Heifers Dairy Cattle Slaughter Feeder Cattle
None
None
None
None
None
None
None
None
N/A
N/A Lower Bird Bacteria TMDLs Pollutant Source Assessment
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3.2 Nonpoint Sources
Nonpoint sources include those sources that cannot be identified as entering the waterbody at a specific location. Bacteria originate from rural, suburban, and urban areas. The following section describes possible major nonpoint sources contributing fecal coliform loading within the Study Area.
These sources include wildlife, various agricultural activities and domesticated animals, land application fields, urban runoff, failing onsite wastewater disposal (OSWD) systems, and domestic pets. For watersheds with no municipal wastewater NPDES facilities (total retention or discharging), nonsupport of PBCR use is caused only by nonpoint sources of bacteria. Watersheds with WWTPs that disinfect their effluents can be expected to not contribute significant bacteria in their discharge, but SSOs within collection systems could contribute. And non-disinfecting municipal WWTPs are expected to contribute bacteria in their effluent discharges as well as from possible SSOs. Therefore, total bacteria loads within a watershed from these latter two examples can be expected to come from a combination of nonpoint source and point source.
Bacteria associated with urban runoff can emanate from humans, wildlife, commercially raised farm animals, and domestic pets. Water quality data collected from streams draining urban communities often show existing concentrations of fecal coliform bacteria at levels greater than a state’s instantaneous standards. A study under USEPA’s National Urban Runoff Project indicated that the average fecal coliform concentration from 14 watersheds in different areas within the United States was approximately 15,000 /100 mL in stormwater runoff (USEPA 1983). Runoff from urban areas not permitted under the MS4 program can be a significant source of fecal coliform bacteria. Water quality data collected from streams draining many nonpermitted communities show existing loads of fecal coliform bacteria at levels greater than the State’s instantaneous standards. Best management practices (BMP) such as buffer strips, repair of leaking sewage collection systems and proper disposal of domestic animal waste can reduce bacteria loading to waterbodies.
3.2.1 Wildlife
Fecal coliform bacteria are produced by all warm-blooded animals, including wildlife such as mammals and birds. In developing bacteria TMDLs it is important to identify the potential for bacteria contributions from wildlife by watershed. Wildlife is naturally attracted to riparian corridors of streams and rivers. With direct access to the stream channel, wildlife can be a concentrated source of bacteria loading to a waterbody. Bacteria from wildlife are also deposited onto land surfaces, where it may be washed into nearby streams by rainfall runoff. Currently there are insufficient data available to estimate populations and spatial distribution of wildlife and avian species by watershed. Consequently it is difficult to assess the magnitude of bacteria contributions from wildlife species as a general category.
However, adequate data are available by county to estimate the number of deer by watershed. This report assumes that deer habitat includes forests, croplands, and pastures. Using Oklahoma Department of Wildlife Conservation county data, the population of deer can be roughly estimated from the actual number of deer harvested and harvest rate estimates. Deer harvest success varies from year to year based on weather and other factors; an estimated annual harvest rate of 20 percent to predict deer population by county was assumed. Using the estimated deer population by county and the percentage of the watershed area within each Lower Bird Bacteria TMDLs Pollutant Source Assessment
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county, a wild deer population can be calculated for each watershed. Table 3-5 provides the estimated number of deer for the watershed.
Table 3-5 Estimated Deer Populations Waterbody ID Waterbody Name Deer Acres
OK121300010010_00
Bird Creek (Lower)
903
114,924
OK121300010090_00
Coal Creek
68
10,517
OK121300010060_00
Ranch Creek
80
12,373
According to a study conducted by ASAE (the American Society of Agricultural Engineers), deer release approximately 5x108 fecal coliform units per animal per day (ASAE 1999). Although only a fraction of the total fecal coliform loading produced by the deer population may actually enter a waterbody, the estimated fecal coliform production for deer provided in Table 3-6 in cfu/day provides a relative magnitude of loading in each watershed.
Table 3-6 Estimated Fecal Coliform Production for Deer Waterbody ID Waterbody Name Watershed Area (acres) Wild Deer Population Estimated Wild Deer per acre Fecal Production (x 108 cfu/day) of Deer Population
OK121300010010_00
Bird Creek (Lower)
114,924
903
0.0079
4,515
OK121300010090_00
Coal Creek
10,517
68
0.0065
340
OK121300010060_00
Ranch Creek
12,373
80
0.006
400
3.2.2 Non-Permitted Agricultural Activities and Domesticated Animals
There are a number of non-permitted agricultural activities that can also be sources of fecal bacteria loading. Agricultural activities of greatest concern are typically those associated with livestock operations (Drapcho and Hubbs 2002). The following are examples of commercial raised farm animal activities that can contribute to bacteria sources: Processed commercially raised farm animal manure is often applied to fields as fertilizer, and can contribute to fecal bacteria loading to waterbodies if washed into streams by runoff. Animals grazing in pastures deposit manure containing fecal bacteria onto land surfaces. These bacteria may be washed into waterbodies by runoff. Animals often have direct access to waterbodies and can provide a concentrated source of fecal bacteria loading directly into streams.
Table 3-7 provides estimated numbers of commercially raised farm animals in the Study Area based on U.S. Department of Agriculture (USDA) county agricultural census data (USDA 2002). These data were provided by ODEQ in spreadsheets. The estimated animal populations in Table 3-7 were derived by using the percentage of the watershed within each county. Because the watershed area in each county is generally much smaller than the county itself, and Lower Bird Bacteria TMDLs Pollutant Source Assessment
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commercially raised farm animals are not evenly distributed across counties or constant with time, these are rough estimates only. Among the animal groups represented, cattle are the most abundant species in the Study Area, generate the largest amount of fecal coliform and often have direct access to the impaired waterbodies or their tributaries.
Detailed information is not available to describe or quantify the relationship between in-stream concentrations of bacteria and land application of manure. The estimated number of each type of animal per acre and total numbers of animal types within the watersheds are shown in Table 3-7. These estimates are also based on the county level reports from the 2002 USDA county agricultural census, and thus represent approximations of the land application area in each watershed. Because of the lack of specific data, land application of animal manure is not quantified in Table 3-7 but is considered a potential source of bacteria loading to the waterbodies in the Study Area. Most poultry feeding operations are regulated by ODAFF, and are required to land apply chicken waste in accordance with their Animal Waste Management Plans or Comprehensive Nutrient Management Plans. While these plans are not designed to control bacteria loading, best management practices and conservation measures, if properly implemented, could greatly reduce the contribution of bacteria from this group of animals to the watershed.
Table 3-7 Commercially Raised Farm Animals and Manure Application Area Estimates by Watershed ANIMAL CATEGORY Bird Creek (Lower) Coal Creek Ranch Creek Cattle & Calves-all
8,262
589
704 Dairy Cows
68
2
3 Horses & Ponies
927
86
102 Goats
11
1
1 Sheep & Lambs
168
18
21 Hogs & Pigs
57
4
4 Ducks & Geese
207
19
23 Chickens & Turkeys
682
0
0 Acres of Manure Application
400
29
34
According to a study conducted by the ASAE, the daily fecal coliform production rates by species were estimated as follows (ASAE 1999): Beef cattle release approximately 1.04E+11 fecal coliform counts per animal per day; Dairy cattle release approximately 1.01E+11 per animal per day Swine release approximately 1.08E+10 per animal per day Chickens release approximately 1.36E+08 per animal per day Sheep release approximately 1.20E+10 per animal per day Horses release approximately 4.20E+08 per animal per day; Turkey release approximately 9.30E+07 per animal per day Lower Bird Bacteria TMDLs Pollutant Source Assessment
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Ducks release approximately 2.43E+09 per animal per day Geese release approximately 4.90E+10 per animal per day
Using the estimated animal populations and the fecal coliform production rates from ASAE, estimates of fecal coliform production from each group of commercially raised farm animals were calculated in Table 3-9 for each watershed in the Study Area. Only a small fraction of these fecal coliform are expected to represent loading into waterbodies, either washed into streams by runoff or by direct deposition from wading animals. Cattle appear to represent the largest potential source of fecal bacteria among the animal groups represented. The animal census data provided by ODAFF showed that there were no contract poultry growers in the Study Area (so indicated in Table 3-8). However, for consistency, estimated fecal coliform production for the general category of poultry based on USDA county agriculture census numbers is summarized in Table 3-9.
Table 3-8 Estimated Poultry Numbers for Contract Growers Inventoried by ODAFF Waterbody ID Waterbody Name County Type Estimated Birds
OK121300010010_00
Bird Creek (Lower)
No growers
None
None
OK121300010090_00
Coal Creek
No growers
None
None
OK121300010060_00
Ranch Creek
No growers
None
None
Table 3-9 Fecal Coliform Production Estimates for Commercially Raised Farm Animals (x109 number/day) ANIMAL CATEGORY Bird Creek (Lower) Coal Creek Ranch Creek
Cattle & Calves-all
859,206
62,235
73,213
Dairy Cows
6,874
245
288
Horses & Ponies
390
36.3
42.7
Sheep & Lambs
2,011
213
250
Hogs & Pigs
621
38.8
45.6
Ducks & Geese
503
46.9
55.1
Chickens & Turkeys
93
0
0
Total
1,382,916
62,815
73,895
3.2.3 Failing Onsite Wastewater Disposal Systems and Illicit Discharges
ODEQ is responsible for implementing the regulations of Title 252, Chapter 641 of the Oklahoma Administrative Code, which defines design standards for individual and small public onsite sewage disposal systems (ODEQ 2004). OSWD systems and illicit discharges can be a source of bacteria loading to streams and rivers. Bacteria loading from failing OSWD systems can be transported to streams in a variety of ways, including runoff from surface ponding or through groundwater. Fecal coliform-contaminated groundwater can also discharge to creeks through springs and seeps.
To estimate the potential magnitude of OSWDs fecal bacteria loading, the number of OSWD systems was estimated for the Lower Bird Creek watershed. The estimate of OSWD Lower Bird Bacteria TMDLs Pollutant Source Assessment
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systems was derived by using data from the 1990 U.S. Census (U.S. Census Bureau 2000) and provided by ODEQ to INCOG. The density of OSWD systems within the watershed was estimated by dividing the number of OSWD systems in each census block by the number of acres in each census block. This density was then applied to the number of acres of each census block within a stream segment watershed. Census blocks crossing a watershed boundary required additional calculation to estimate the number of OSWD systems based on the proportion of the census tracts falling within each watershed. This step involved adding all OSWD systems for each whole or partial census block.
Over time, most OSWD systems operating at full capacity will fail. OSWD system failures are proportional to the adequacy of a state’s minimum design criteria (Hall 2002). The 1995 American Housing Survey conducted by the U.S. Census Bureau estimates that, nationwide, 10 percent of occupied homes with OSWD systems experience malfunctions during the year (U.S. Census Bureau 1995). A study conducted by Reed, Stowe & Yanke, LLC (2001) reported that approximately 12 percent of the OSWD systems in East Texas were chronically malfunctioning. Most studies estimate that the minimum lot size necessary to ensure against contamination is roughly one-half to one acre (Hall 2002). Some studies, however, found that lot sizes in this range or even larger could still cause contamination of ground or surface water (University of Florida 1987). It is estimated that areas with more than 40 OSWD systems per square mile (6.25 septic systems per 100 acres) can be considered to have potential contamination problems (Canter and Knox 1986). Table 3-10 summarizes estimates of sewered and unsewered households for the Study Area.
For the purpose of estimating fecal coliform loading in watersheds, an OSWD failure rate of 12 percent was used. Using this 12 percent failure rate, calculations were made to characterize fecal coliform loads in each watershed.
Fecal coliform loads were estimated using the following equation (USEPA 2001):
galmlhouseholdpersonpersondaygalmlcountssystemsFailingdaycounts2.3785#7010010##6
Table 3-10 Estimates of Sewered and Unsewered Households Waterbody ID Waterbody Name Public Sewer Septic Tank Other Means Housing Units % Sewered
OK121300010010_00
Bird Creek (Lower)
83,406
4,120
141
87,667
95.1%
OK121300010090_00
Coal Creek
15,430
216
7
15,653
98.6%
OK121300010060_00
Ranch Creek
1,047
441
0
1,515
70.9%
The average of number of people per household was calculated to be 2.4 for counties in the Study Area (U.S. Census Bureau 2000). Approximately 70 gallons of wastewater were estimated to be produced on average per person per day (Metcalf and Eddy 1991). The fecal coliform concentration in septic tank effluent was estimated to be 106 per 100 mL of effluent based on reported concentrations from a number of published reports (Metcalf and Eddy 1991; Canter and Knox 1985; Cogger and Carlile 1984). Using this information, the estimated load from failing septic systems within each of the watersheds was summarized below in Table 3 11. Lower Bird Bacteria TMDLs Pollutant Source Assessment
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Table 3-11 Estimated Fecal Coliform Load from OSWD Systems Waterbody ID Waterbody Name Acres Septic Tank # of Failing Septic Tanks Estimated Loads from Septic Tanks (x 109 counts/day)
OK121300010010_00
Bird Creek (Lower)
114,924
4,120
494
0.6
OK121300010090_00
Coal Creek
10,517
216
26
0.03
OK121300010060_00
Ranch Creek
12,373
441
53
0.06
3.2.4 Domestic Pets
Fecal matter from dogs and cats is transported to streams by runoff from urban and suburban areas and can be a potential source of bacteria loading. On average nationally, there are 1.7 dogs per household and 2.2 cats per household (American Veterinary Medical Association 2007). Using the U.S. Census data at the block level (U.S. Census Bureau 2000), dog and cat populations can be estimated for each watershed. Table 3-12 summarizes the estimated number of dogs and cats for the Study Area.
Table 3-12 Estimated Numbers of Pets Waterbody ID Waterbody Name Dogs Cats
OK121300010010_00
Bird Creek (Lower)
367,197
475,197
OK121300010090_00
Coal Creek
58,017
75,080
OK121300010060_00
Ranch Creek
8,758
11,333
Table 3-13 provides an estimate of the fecal coliform load from pets. These estimates are based on estimated fecal coliform production rates of 5.4x108 per day for cats and 3.3x109 per day for dogs (Schueler 2000).
Table 3-13 Estimated Fecal Coliform Daily Production by Pets (x 109) Waterbody ID Waterbody Name Dogs Cats Total
OK121300010010_00
Bird Creek (Lower)
1,211,750
256,606
1,468,357
OK121300010090_00
Coal Creek
191,456
40,543
231,999
OK121300010060_00
Ranch Creek
28,901
6,120
35,021
3.3 Summary of Bacteria Sources
Table 3-14 summarizes the suspected sources of bacteria loading in each impaired watershed. There are three municipal WWTP NPDES-permitted discharge facilities present in the watershed, and all three presently disinfect their effluent. Therefore, nonsupport of the PBCR use is likely caused mainly by nonpoint sources or other point sources. For example, it can be expected that the large MS4 areas in the watersheds result in MS4 point source loadings. Lower Bird Bacteria TMDLs Pollutant Source Assessment
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Table 3-14 Estimated Major Source of Bacteria Loading by Watershed Waterbody ID Waterbody Name Point Sources Nonpoint Sources Major Source
OK121300010010_00
Bird Creek (Lower)
Yes
Yes
Nonpoint/point
OK121300010090_00
Coal Creek
No
Yes
Nonpoint/point
OK121300010060_00
Ranch Creek
No
Yes
Nonpoint/point
Table 3-15 below provides a summary of the estimated fecal coliform loads in percentage for the four major nonpoint source categories (commercially raised farm animals, pets, deer, and septic tanks) that are contributing to the elevated bacteria concentrations in each watershed. In the entire Lower Bird Creek watershed, pets and commercially raised farm animals are estimated to be the primary contributors of fecal coliform loading to land surfaces with pets being slightly more significant. In the urban landuses dominated Coal Creek watershed, pets are the primary sources while in the much less urbanized Ranch Creek watershed, commercially raised farm animals contribute the most.
It must be noted that while no data are available to estimate populations and fecal loading of wildlife other than deer, a number of bacteria source tracking studies demonstrate that wild birds and mammals represent a major source of the fecal bacteria found in streams. If fecal coliform loads from other wildlife could be included in Table 3-15, the percent loads of the two largest nonpoint estimates (farm animals and pets) would be lower proportional to the amount of loads that would be calculated for wildlife.
The magnitude of loading to a stream may not be reflected in the magnitude of loading to land surfaces. While no studies quantify these effects, bacteria may die off or survive at different rates depending on the manure characteristics and a number of other environmental conditions. Manure handling practices, use of BMPs, and relative location to streams can also affect stream loading. Also, the structural properties of some manure, such as cow patties, may limit their wash off into streams by runoff.
If poultry litter is applied to areas in the watershed in a pulverized form, it could be a larger source during storm runoff events. The Shoal Creek report by the Missouri Department of Natural Resources showed that poultry litter was about 71% of the high flow load and cow pats contributed only about 28% of it (MDNR, 2003). The Shoal Creek report also showed that poultry litter was insignificant under low flow conditions up to 50% frequency. In contrast, malfunctioning septic tank effluent may be present in pooled water on the surface, or in shallow groundwater, which may enhance its conveyance to streams.
Table 3-15 Summary of Fecal Coliform Load Estimates from Nonpoint Sources to Land Surfaces Waterbody ID Waterbody Name Commercially Raised Farm Animals Pets Deer Estimated Loads from Septic Tanks
OK121300010010_00
Bird Creek (Lower)
48.5%
51.5%
0.0%
0.0%
OK121300010090_00
Coal Creek
21.3%
78.7%
0.0%
0.0%
OK121300010060_00
Ranch Creek
67.8%
32.1%
0.0%
0.0%
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SECTION 4 TECHNICAL APPROACH AND METHODS
The objective of a TMDL is to estimate allowable pollutant loads and to allocate these loads to the known pollutant sources in the watershed so appropriate control measures can be implemented and the WQS achieved. A TMDL is expressed as the sum of three elements as described in the following mathematical equation:
TMDL = Σ WLA + Σ LA + MOS
The WLA is the portion of the TMDL allocated to existing and future point sources. The LA is the portion of the TMDL allocated to nonpoint sources, including natural background sources. The MOS is intended to ensure that WQS will be met. Thus, the allowable pollutant load that can be allocated to point and nonpoint sources can then be defined as the TMDL minus the MOS.
40 CFR, §130.2(1), states that TMDLs can be expressed in terms of mass per time, toxicity, or other appropriate measures. For fecal coliform, E. coli, or Enterococci bacteria, TMDLs are expressed as colony-forming units per day, where possible, or as a percent reduction goal (PRG), and represent the maximum one-day load the stream can assimilate while still attaining the WQS.
4.1 Using Load Duration Curves to Develop TMDLs
The TMDL calculations presented in this report are derived from load duration curves (LDC). LDCs facilitate rapid development of TMDLs, and as a TMDL development tool, are effective at identifying whether impairments are associated with point or nonpoint sources. The technical approach for using LDCs for TMDL development includes the four following steps that are described in Subsections 4.2 through 4.4 below: Preparing flow duration curves for gaged and ungaged stream segments; Estimating existing bacteria loading in the receiving water using ambient water quality data; Using LDCs to identify the critical condition that will dictate loading reductions necessary to attain WQS; and Interpreting LDCs to derive TMDL elements – WLA, LA, MOS, and PRG.
Historically, in developing WLAs for pollutants from point sources, it was customary to designate a critical low flow condition (e.g., 7Q2) at which the maximum permissible loading was calculated. As water quality management efforts expanded in scope to quantitatively address nonpoint sources of pollution and types of pollutants, it became clear that this single critical low flow condition was inadequate to ensure adequate water quality across a range of flow conditions. Use of the LDC obviates the need to determine a design storm or selected flow recurrence interval with which to characterize the appropriate flow level for the assessment of critical conditions. For waterbodies impacted by both point and nonpoint sources, the “nonpoint source critical condition” would typically occur during high flows, when rainfall runoff would contribute the bulk of the pollutant load, while the “point source critical condition” would typically occur during low flows, when WWTP effluents would dominate the base flow of the impaired water. However, violations that occur during low flows may not be Lower Bird Bacteria TMDLs Technical Approach and Methods
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caused exclusively by point sources. Violations have been noted in some watersheds that contain no point sources. Research has shown that bacteria loading in streams during low flow conditions may be due to direct deposit of cattle manure into streams and faulty septic tank/lateral field systems.
LDCs display the maximum allowable load over the complete range of flow conditions by a line using the calculation of flow multiplied by the water quality criterion. The TMDL can be expressed as a continuous function of flow, equal to the line, or as a discrete value derived from a specific flow condition.
4.2 Development of Flow Duration Curves
Flow duration curves (FDCs) serve as the foundation of LDCs and are graphical representations of the flow characteristics of a stream at a given site. Flow duration curves utilize the historical hydrologic record from stream gages to forecast future recurrence frequencies. Many streams throughout Oklahoma do not have long term flow data and therefore flow frequencies must be estimated. The most basic method to estimate flows at an ungaged site involves 1) identifying an upstream or downstream flow gage; 2) calculating the contributing drainage areas of the ungaged sites and the flow gage; and 3) calculating daily flows at the ungaged site by using the flow at the gaged site multiplied by the drainage area ratio. A more complex approach also considers watershed differences in rainfall, land use, and the hydrologic properties of soil that govern runoff and retention. More than one upstream flow gage may also be considered. A more detailed explanation of the methods for estimating flow at ungaged streams stations is provided in Appendix C.
Flow duration curves are a type of cumulative distribution function. The flow duration curve represents the fraction of flow observations that exceed a given flow at the site of interest. The observed flow values are first ranked from highest to lowest then, for each observation, the percentage of observations exceeding that flow is calculated. The flow value is read from the ordinate (y-axis), which is typically on a logarithmic scale since the high flows would otherwise overwhelm the low flows. The flow exceedance frequency is read from the abscissa (x-axis), which is numbered from 0 to 100 percent, and may or may not be logarithmic. The lowest measured flow occurs at an exceedance frequency of 100 percent indicating that flow has equaled or exceeded this value 100 percent of the time, while the highest measured flow is found at an exceedance frequency of 0 percent. The median flow occurs at a flow exceedance frequency of 50 percent. The flow exceedance percentiles for Lower Bird Creek addressed in this report are provided in Appendix C.
While the number of observations required to develop a flow duration curve is not rigorously specified, a flow duration curve is usually based on more than 1 year of observations, and encompasses inter-annual and seasonal variation. Ideally, the drought of record and flood of record are included in the observations. For this purpose, the long-term flow gaging stations operated by the USGS are utilized (USGS 2007a).
A typical semi-log flow duration curve exhibits a sigmoidal shape, bending upward near a flow exceedance frequency value of 0 percent and downward at a frequency near 100 percent, often with a relatively constant slope in between. For sites that on occasion exhibit no flow, the curve will intersect the abscissa at a frequency less than 100 percent. As the number of observations at a site increases, the line of the LDC tends to appear smoother. However, at Lower Bird Bacteria TMDLs Technical Approach and Methods
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extreme low and high flow values, flow duration curves may exhibit a “stair step” effect due to the USGS flow data rounding conventions near the limits of quantification.
4.3 Estimating Current Point and Nonpoint Loading
Another key step in the use of LDCs for TMDL development is the estimation of existing bacteria loading from point and nonpoint sources and the display of this loading in relation to the TMDL. In Oklahoma, WWTPs that discharge treated sanitary wastewater must meet the state WQS for fecal bacteria at the point of discharge. However, for TMDL analysis it is necessary to understand the relative contribution of WWTPs to the overall pollutant loading and its general compliance with required effluent limits. The monthly bacteria load for continuous point source dischargers is estimated by multiplying the monthly average flow rates by the monthly geometric mean using a conversion factor. The current pollutant loading from each permitted point source discharge is calculated using the equation below.
Point Source Loading = monthly average flow rates (mgd) * geometric mean of corresponding fecal coliform concentration * unit conversion factor
Where:
unit conversion factor = 37,854,120 100-ml/million gallons (mg)
It is difficult to estimate current nonpoint loading due to lack of specific water quality and flow information that would assist in estimating the relative proportion of non-specific sources within the watershed. Therefore, existing in-stream loads minus the point source loads were used as an estimate for nonpoint loading.
4.4 Development of TMDLs Using Load Duration Curves
The final step in the TMDL calculation process involves a group of additional computations derived from the preparation of LDCs. These computations are necessary to derive a PRG (which is one method of presenting how much bacteria loading must be reduced to meet WQS in the impaired watershed).
Step 1: Generate Bacteria LDCs. LDCs are similar in appearance to flow duration curves; however, the ordinate is expressed in terms of a bacteria load in cfu/day. The curve represents the single sample water quality criterion for fecal coliform (400 cfu/100 mL), E. coli (406 cfu/100 mL), or Enterococci (108 cfu/100 mL) expressed in terms of a load through multiplication by the continuum of flows historically observed at this site. The basic steps to generating an LDC involve: obtaining daily flow data for the site of interest from the USGS; sorting the flow data and calculating flow exceedance percentiles for the time period and season of interest; obtaining the water quality data from the primary contact recreation season (May 1 through September 30); matching the water quality observations with the flow data from the same date; display a curve on a plot that represents the allowable load multiplied by the actual or estimated flow by the WQS for each respective indicator; Lower Bird Bacteria TMDLs Technical Approach and Methods
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multiplying the flow by the water quality parameter concentration to calculate daily loads; then plotting the flow exceedance percentiles and daily load observations in a load duration plot.
The culmination of these steps is expressed in the following formula, which is displayed on the LDC as the TMDL curve:
TMDL (cfu/day) = WQS * flow (cfs) * unit conversion factor
Where: WQS = 400 cfu /100 ml (Fecal coliform); 406 cfu/100 ml (E. coli); or 108 cfu/100 ml (Enterococci)
unit conversion factor = 24,465,525 ml*s / ft3*day
The flow exceedance frequency (x-value of each point) is obtained by looking up the historical exceedance frequency of the measured or estimated flow; in other words, the percent of historical observations that equal or exceed the measured or estimated flow. Historical observations of bacteria concentration are paired with flow data and are plotted on the LDC. The fecal coliform load (or the y-value of each point) is calculated by multiplying the fecal coliform concentration (cfu/100 mL) by the instantaneous flow (cubic feet per second [cfs]) at the same site and time, with appropriate volumetric and time unit conversions. Fecal coliform/E. coli/Enterococci loads representing exceedance of water quality criteria fall above the water quality criterion line.
Only those flows and water quality samples observed in the months comprising the primary contact recreation season are used to generate the LDCs. It is inappropriate to compare single sample bacteria observations and instantaneous or daily flow durations to a 30-day geometric mean water quality criterion in the LDC.
As noted earlier, runoff has a strong influence on loading of nonpoint pollution. Yet flows do not always correspond directly to local runoff; high flows may occur in dry weather and runoff influence may be observed with low or moderate flows.
Step 2: Define MOS. The MOS may be defined explicitly or implicitly. A typical explicit approach would reserve some fraction of the TMDL (e.g., 10%) as the MOS. In an implicit approach, conservative assumptions used in developing the TMDL are relied upon to provide an MOS to assure that WQS are attained.
For the TMDLs in this report, an explicit MOS of 10 percent of the TMDL value (10% of the instantaneous water quality criterion) has been selected.
Step 3: Calculate WLA. As previously stated, the pollutant LA for point sources is defined by the WLA. A point source can be either a wastewater (continuous) or stormwater (MS4) discharge. Stormwater point sources are typically associated with urban and industrialized areas, and recent USEPA guidance includes NPDES-permitted stormwater discharges as point source discharges and, therefore, part of the WLA.
The LDC approach recognizes that the assimilative capacity of a waterbody depends on the flow, and that maximum allowable loading will vary with flow condition. This LDC approach meets the requirements of 40 CFR, 130.2(i) for expressing TMDLs “in terms of mass per time, Lower Bird Bacteria TMDLs Technical Approach and Methods
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toxicity, or other appropriate measures” and is consistent with USEPA’s Protocol for Developing Pathogen TMDLs (USEPA 2001).
WLA for WWTP. WLAs may be set to zero for watersheds with no existing or planned continuous permitted point sources. For watersheds with permitted point sources, NPDES permit limits are used to derive WLAs. The permitted average flow rate used for each point source discharge and the water quality criterion concentration defined in the permit are used to estimate the WLA for each wastewater facility. In cases where a permitted flow rate is not available for a WWTP, then the average of monthly flow rates derived from DMRs can be used. WLA values from all NPDES wastewater dischargers are then summed to represent the total WLA for the watershed. Using this information bacteria WLAs can be calculated using a mass balance approach as shown in the equation below.
WLA = WQS * flow * unit conversion factor (#/day)
Where:
Where: WQS = 200 cfu /100 ml (Fecal coliform); 126 cfu/100 ml (E. coli); or 33 cfu/100 ml (Enterococci)
flow (106 gal/day) = permitted flow
unit conversion factor = 37,854,120-106gal/day
Step 4: Calculate LA and WLA for MS4s. Given the lack of data and the variability of storm events and discharges from storm sewer system discharges, it is difficult to establish numeric limits on stormwater discharges that accurately address projected loadings. As a result, EPA regulations and guidance recommend expressing NPDES permit limits for MS4s as BMPs.
LAs can be calculated under different flow conditions as the water quality target load minus the WLA. The LA is represented by the area under the LDC but above the WLA. The LA at any particular flow exceedance is calculated as shown in the equation below.
LA = TMDL - WLA_WWTP - WLA_MS4 - MOS
WLA for MS4s. If there are no permitted MS4s in the study area, WLA_MS4 is set to zero. When there are permitted MS4s in the watershed, we can first calculate the sum of LA + WLA_MS4 using the above formula, then separate WLA for MS4s from the sum based on the percentage of a watershed that is under a MS4 jurisdiction. This WLA for MS4s may not be the total load allocated for permitted MS4s unless the whole MS4 area is located within the study watershed boundary. However, in most cases the study watershed intersects only a portion of the permitted MS4 coverage areas.
Step 5: Estimate WLA Load Reduction. The WLA load reduction was not calculated as it was assumed that continuous dischargers (NPDES-permitted WWTPs) are adequately regulated under existing permits to achieve water quality standards at the end-of-pipe and, therefore, no WLA reduction would be required. All SSOs are considered unpermitted discharges under State statute and DEQ regulations. For any MS4s that are located within a watershed requiring a TMDL the load reduction will be equal to the PRG established for the overall watershed. Lower Bird Bacteria TMDLs Technical Approach and Methods
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Step 6: Estimate LA Load Reduction. After existing loading estimates are computed for each bacteria indicator, nonpoint load reduction estimates for each stream segment are calculated by using the difference between estimated existing loading and the allowable load expressed by the LDC (TMDL-MOS). This difference is expressed as the overall percent reduction goal for the impaired waterbody. For fecal coliform the PRG which ensures that no more than 25 percent of the samples exceed the TMDL based on the instantaneous criteria allocates the loads in manner that is also protective of the geometric mean criterion. For E. coli and Enterococci, because WQ standards are considered to be met if 1) either the geometric mean of all data is less than the geometric mean criteria, or 2) no sample exceeds the instantaneous criteria, the TMDL PRG will be the lesser of that required to meet the geometric mean or instantaneous criteria.
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SECTION 5 TMDL CALCULATIONS
5.1 Flow Duration Curves
Following the same procedures described in Section 4.3, Figures 4-1 to 4-3 are the flow duration curves developed for the studied stream segments. The flow duration curve for the Lower Bird Creek (OK121200010010_00) was based on measured flows at USGS gage station 07178200 (Bird Creek near Catoosa, OK). This gage is co-located with WQM station OK121300010010-001AT. The flow period used for this station was January 1, 1990 through August 16, 2009. This is the period of record represented by the current dam impoundments in the Bird Creek watershed.
The flow duration curve for the Coal Creek (OK121300010090_00) was based on measured flows at USGS gage station 07177800 (Coal Creek at Tulsa, OK). The gage is co-located with OCC WQM station OK121300-01-0090M. The flow period used for this station was January 30, 1988 through September 30, 2009.
No flow gage exists on Ranch Creek (OK121300010060_00). Therefore, flows for this waterbody were projected using the watershed area ratio method based on measured flows at USGS gage station 07177800 (Coal Creek at Tulsa, OK). The flow period used for this station was January 30, 1988 through September 30, 2009.
Figure 5-1
Primary Season Flow Duration Curve0.11.010.0100.01,000.010,000.0100,000.00%10%20%30%40%50%60%70%80%90%100%Flow Duration IntervalFlow (cfs)Bird Creek near CatoosaHighFlowsLowFlowsDry ConditionsMid-rangeFlowsMoist Conditions412.43,302.0202.0262.0cfscfscfscfsLower Bird Bacteria TMDLs TMDL Calculations
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Figure 5-2
Figure 5-3
0.11.010.0100.01,000.00%10%20%30%40%50%60%70%80%90%100%Flow (cfs)Flow Duration IntervalPrimary Season Flow Duration CurveCoal CreekHighFlowsLowFlowsDry ConditionsMid-rangeFlowsMoist Conditions2.520.00.31.4cfscfscfscfs0.11.010.0100.01,000.010,000.00%10%20%30%40%50%60%70%80%90%100%Flow (cfs)Flow Duration IntervalPrimary Season Flow Duration CurveRanch CreekHighFlowsLowFlowsDry ConditionsMid-rangeFlowsMoist Conditions6.451.30.73.6cfscfscfscfsLower Bird Bacteria TMDLs TMDL Calculations
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5.2 Estimated Loading and Critical Conditions
Load Duration Curves: USEPA regulations at 40 CFR 130.7(c)(1) require TMDLs to take into account critical conditions for stream flow, loading, and all applicable water quality standards. To accomplish this, available in-stream WQM data were evaluated with respect to flows and magnitude of water quality criteria exceedance using LDCs.
To calculate the bacteria load at the WQS, the flow rate at each flow exceedance percentile is multiplied by a unit conversion factor (24,465,525 ml*s / ft3*day) and the criterion specific to each bacteria indicator. This calculation produces the maximum bacteria load in the stream without exceeding the instantaneous standard over the range of flow conditions. The x-axis indicates the flow exceedance percentile, while the y-axis is expressed in terms of a bacteria load.
To estimate existing loading, bacteria observations for the primary contact recreation season (May 1st through September 30th) are paired with the flows measured or estimated in that segment on the same date. Pollutant loads are then calculated by multiplying the measured bacteria concentration by the flow rate and a unit conversion factor of 24,465,525 ml*s / ft3*day. The associated flow exceedance percentile is then matched with the measured or projected flow from the tables provided in Appendix C. The observed bacteria loads are then added to the LDC plot as points. These points represent individual ambient water quality samples of bacteria. Points above the LDC indicate the bacteria instantaneous standard was exceeded at the time of sampling. Conversely, points under the LDC indicate the sample met the WQS.
A subset of the LDCs for each impaired waterbody is shown in Figures 5-4 through 5-6. While some waterbodies may be listed for multiple bacterial indicators, only one LDC for each waterbody is presented in Figures 5-4 through 5-6 – the LDC for the bacterial indicator that has the largest PRG (Table 5-1). The LDCs for the other bacterial indicators that require TMDLs are presented in Subsection 5.7 of this report.
The LDC for Lower Bird Creek segment OK121300010010_00 (Figure 5-4) is based on Enterococcus bacteria measurements during the primary contact recreation season at WQM station OK121300010010-001AT. The LDC indicates that Enterococcus levels exceed the instantaneous water quality criteria during all flow conditions except high flows. Exceedances during non-dry conditions are thought to be due to non-point sources. The exceedances found during dry weather conditions indicate some level of pollution may be due to failing onsite systems or direct deposition of animal manure.
The LDC for Coal Creek (OK121300010090_00, Figure 5-5) is based on E. Coli bacteria measurements during the primary contact recreation season at WQM station OK121300-01-0090M. The LDC indicates that E. Coli levels exceed the instantaneous water quality criteria during mid-flow to moist conditions. Exceedances during non-dry conditions are thought to be due to non-point sources.
The LDC for Ranch Creek (OK121300010060_00, Figure 5-6) is based on E. Coli bacteria measurements during the primary contact recreation season at WQM station OK121300-01-0060G. The LDC indicates that E. Coli levels exceed the instantaneous water quality criteria during mid-flow to moist conditions. Exceedances during non-dry conditions are thought to be due to non-point sources. Lower Bird Bacteria TMDLs TMDL Calculations
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Figure 5-4
Figure 5-5
Primary Season Enterococci Load Duration Curve1.0E-021.0E-011.0E+001.0E+011.0E+021.0E+031.0E+041.0E+051.0E+061.0E+071.0E+080102030405060708090100Flow Duration Interval (%)Bacteria Counts (109-org./day)TMDL Load DurationPrimary Season DataFlow Range DivideWLA-WTTPBird Creek near CatoosaHighFlowsLowFlowsDry ConditionsMid-range FlowsMoist Conditions20062006-Monitoring Data()1.0E-021.0E-011.0E+001.0E+011.0E+021.0E+031.0E+041.0E+051.0E+061.0E+071.0E+080102030405060708090100E. Coli Counts (109-org./day)Flow Duration Interval (%)Primary Season E. Coli Load Duration CurveTMDL Load DurationPrmiary Season DataFlow Range DivideWLA-WTTPCoal CreekHighFlowsLowFlowsDry ConditionsMid-range FlowsMoist Conditions20032005-Monitoring Data()Lower Bird Bacteria TMDLs TMDL Calculations
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Figure 5-6
Establishing Percent Reduction Goals: The LDC approach recognizes that the assimilative capacity of a waterbody depends on the flow, and that maximum allowable loading varies with flow condition. Existing loading, and load reductions required to meet the TMDL water quality target can also be calculated under different flow conditions. The difference between existing loading and the water quality target is used to calculate the loading reductions required. Percent Reduction Goals (PRGs) are calculated for each watershed and bacterial indicator species. This is because for the PBCR use to be supported, criteria for each bacteria indicator must be met in each impaired waterbody.
Table 5-1 presents the percent reductions necessary for each bacteria indicator in the waterbodies in the Study Area. Attainment of WQS in response to TMDL implementation will be based on future results measured within the stream segment. The appropriate PRG for each bacteria indicator for each waterbody in Table 5-1 is denoted by the bold text. The PRGs range from 44.8 to 82.6 percent. Because the Coal and Ranch Creeks are tributaries to the Lower Bird Creek and the load reduction goals for the Coal and Ranch Creeks are either equal or smaller than that for the Lower Bird Creek for E. Coli, the more restrictive load reduction goal of 44.8% for the Lower Bird Creek will apply to these two tributaries.
1.0E-021.0E-011.0E+001.0E+011.0E+021.0E+031.0E+041.0E+051.0E+061.0E+071.0E+080102030405060708090100E. Coli Counts (109-org./day)Flow Duration Interval (%)Primary Season E. Coli Load Duration CurveTMDL Load DurationPrmiary Season DataFlow Range DivideWLA-WTTPRanch CreekHighFlowsLowFlowsDry ConditionsMid-range FlowsMoist Conditions20032005-Monitoring Data()Lower Bird Bacteria T